fixed parentheses issue harsh98trivedi#29

Author: shail-patel-321

calc.js

@@ -41,7 +41,14 @@ for (item of buttons) {
       } else {
         screen.classList.remove("negative");
       }
-    } else if (isNumber(buttonText)) {
+    } else if(buttonText=="(" || buttonText==")") {
+      if(flag==1){
+        flag =0;
+      }
+      screenValue+=buttonText;
+      screen.value=screenValue;
+    } 
+    else if (isNumber(buttonText)) {
       if (flag == 1) {
         screenValue = buttonText;
         flag = 0;