Gammar edit (ziishaned#96)

Added is to section 4.2

Author: danieloi

README.md

@@ -421,7 +421,7 @@ or `the` which are followed by the word `fat`.
 ### 4.2 Negative Lookahead
 
 Negative lookahead is used when we need to get all matches from input string
-that are not followed by a pattern. Negative lookahead defined same as we define
+that are not followed by a pattern. Negative lookahead is defined same as we define
 positive lookahead but the only difference is instead of equal `=` character we
 use negation `!` character i.e. `(?!...)`. Let's take a look at the following
 regular expression `(T|t)he(?!\sfat)` which means: get all `The` or `the` words