addressed PR feedback

Author: vladima

src/compiler/checker.ts

@@ -15477,7 +15477,7 @@ namespace ts {
                 if (prop.kind === SyntaxKind.ShorthandPropertyAssignment && !inDestructuring && (<ShorthandPropertyAssignment>prop).objectAssignmentInitializer) {
                     // having objectAssignmentInitializer is only valid in ObjectAssignmentPattern
                     // outside of destructuring it is a syntax error
-                    return grammarErrorOnNode((<ShorthandPropertyAssignment>prop).equalsToken, Diagnostics.can_only_be_used_in_object_literal_properties_inside_destructuring_assignment);
+                    return grammarErrorOnNode((<ShorthandPropertyAssignment>prop).equalsToken, Diagnostics.can_only_be_used_in_an_object_literal_property_inside_a_destructuring_assignment);
                 }
 
                 // ECMA-262 11.1.5 Object Initialiser

src/compiler/diagnosticMessages.json

@@ -800,7 +800,7 @@
         "category": "Error",
         "code": 1311
     },
-    "'=' can only be used in object literal properties inside destructuring assignment.": {
+    "'=' can only be used in an object literal property inside a destructuring assignment.": {
         "category": "Error",
         "code": 1312
     },    

tests/baselines/reference/shorthandPropertyAssignmentsInDestructuring.errors.txt

@@ -13,7 +13,7 @@ tests/cases/compiler/shorthandPropertyAssignmentsInDestructuring.ts(87,19): erro
   Types of property 'x' are incompatible.
     Type 'number' is not assignable to type 'string'.
 tests/cases/compiler/shorthandPropertyAssignmentsInDestructuring.ts(113,12): error TS2304: Cannot find name 's'.
-tests/cases/compiler/shorthandPropertyAssignmentsInDestructuring.ts(113,14): error TS1312: '=' can only be used in object literal properties inside destructuring assignment.
+tests/cases/compiler/shorthandPropertyAssignmentsInDestructuring.ts(113,14): error TS1312: '=' can only be used in an object literal property inside a destructuring assignment.
 
 
 ==== tests/cases/compiler/shorthandPropertyAssignmentsInDestructuring.ts (12 errors) ====
@@ -157,7 +157,7 @@ tests/cases/compiler/shorthandPropertyAssignmentsInDestructuring.ts(113,14): err
     	          ~
 !!! error TS2304: Cannot find name 's'.
     	            ~
-!!! error TS1312: '=' can only be used in object literal properties inside destructuring assignment.
+!!! error TS1312: '=' can only be used in an object literal property inside a destructuring assignment.
     });
 
     function foo({a = 4, b = { x: 5 }}) {

tests/baselines/reference/shorthandPropertyAssignmentsInDestructuring_ES6.errors.txt

@@ -13,7 +13,7 @@ tests/cases/compiler/shorthandPropertyAssignmentsInDestructuring_ES6.ts(87,19):
   Types of property 'x' are incompatible.
     Type 'number' is not assignable to type 'string'.
 tests/cases/compiler/shorthandPropertyAssignmentsInDestructuring_ES6.ts(113,12): error TS2304: Cannot find name 's'.
-tests/cases/compiler/shorthandPropertyAssignmentsInDestructuring_ES6.ts(113,14): error TS1312: '=' can only be used in object literal properties inside destructuring assignment.
+tests/cases/compiler/shorthandPropertyAssignmentsInDestructuring_ES6.ts(113,14): error TS1312: '=' can only be used in an object literal property inside a destructuring assignment.
 
 
 ==== tests/cases/compiler/shorthandPropertyAssignmentsInDestructuring_ES6.ts (12 errors) ====
@@ -157,7 +157,7 @@ tests/cases/compiler/shorthandPropertyAssignmentsInDestructuring_ES6.ts(113,14):
     	          ~
 !!! error TS2304: Cannot find name 's'.
     	            ~
-!!! error TS1312: '=' can only be used in object literal properties inside destructuring assignment.
+!!! error TS1312: '=' can only be used in an object literal property inside a destructuring assignment.
     });
 
     function foo({a = 4, b = { x: 5 }}) {