Merge pull request #195 from Mehraddev/patch-2

fix grammar.md

Author: bowbahdoe

src/strings_ii/strip_extra_whitespace.md

@@ -1,6 +1,6 @@
 # Strip extra whitespace
 
-If you have a `String` which might contains some "trailing" whitespace or "leading"
+If you have a `String` which might contain some "trailing" whitespace or "leading"
 whitespace, you can remove that by using the `.strip` method.
 
 This will give a new `String` with both the leading and trailing whitespace removed.
@@ -36,4 +36,4 @@ void main() {
 }
 ```
 
-All of these methods are useful when you get input from human beings. Humans are generally pretty bad at seeing if they hit the spacebar one too many times.
+All of these methods are useful when you get input from human beings. Humans are generally pretty bad at seeing if they hit the spacebar one too many times.