Update PatternMatching.md

Fix grammatical errors in documentation.

courses/Recipes/BasicProgramming/PatternMatching/PatternMatching.md

@@ -21,7 +21,7 @@ Pattern matching is _the_ mechanism for case distinction
 ([Switch]((Rascal:Statements-Switch)) statement) and search ([Visit]((Rascal:Expressions-Visit)) statement) in Rascal. 
 Patterns can also be used in an explicit match operator `:=` and can then be part of larger boolean expressions. 
 Since a pattern match may have more than one solution, local backtracking over the alternatives of a match is provided. 
-Patterns can also be used in [Enumerators]((Rascal:Boolean-Enumerator))s and control structures like 
+Patterns can also be used in [Enumerators]((Rascal:Boolean-Enumerator)) and control structures like 
 [For]((Rascal:Statements-For)) and [While]((Rascal:Statements-While)) statement.
 
 A very rich pattern language is provided that includes string matching based on regular expressions, 
@@ -47,7 +47,7 @@ Regular expressions follow the Java regular expression syntax with one exception
 <_Name_:_RegularExpression_>
 ```
 
-If `RegularExpression` matches, the matched substring is assigned to string variable `Name`.
+If `RegularExpression` matches, the matched substring is assigned to the string variable `Name`.
 
 The following abstract pattern matches the abstract syntax of a while statement defined earlier: