Fix typos (documentationjs#132)

Author: sjsyrek

language/Type-Classes.md

@@ -2,9 +2,9 @@
 
 PureScript supports type classes via the `class` and `instance` keywords.
 
-Types appearing in class instances are must be of the form `String`, `Number`, `Boolean`, or `C t1 ... tn` where `C` is a type constructor (including `->` and `t_i` are types of the same form).
+Types appearing in class instances must be of the form `String`, `Number`, `Boolean`, or `C t1 ... tn` where `C` is a type constructor (including `->` and `t_i` are types of the same form).
 
-Type class instances are resolved based on the order in which they appeared in the source files. Overlapping instances are currently permitted but not recommended. In simple cases the compiler will display a warning and list the instances it found and which was chosen. In the future they may be disallowed completely.
+Type class instances are resolved based on the order in which they appear in the source files. Overlapping instances are currently permitted but not recommended. In simple cases the compiler will display a warning and list the instances it found and which was chosen. In the future, they may be disallowed completely.
 
 Here is an example of the `Show` typeclass, with instances for `String`, `Boolean` and `Array`:
 
@@ -80,7 +80,6 @@ In fact, a type similar to this `AddInt` is provided in `Data.Monoid.Additive`,
 
 For multi-parameter type classes, the orphan instance check requires that the instance is either in the same module as the class, or the same module as at least one of the types occurring in the instance. (TODO: example)
 
-
 ## Functional Dependencies
 
 TODO. For now, see the section in [PureScript by Example](https://leanpub.com/purescript/read#leanpub-auto-functional-dependencies).