Re #6660 Fix typographical errors

Author: mpilgrem

CONTRIBUTING.md

@@ -336,7 +336,7 @@ entry and
 [documentation](https://github.com/commercialhaskell/stack/tree/master/doc/)
 updates with your pull request.
 
-## Backwards Compatability
+## Backwards Compatibility
 
 The Stack package provides a library and an executable (`stack`) that depends on
 the library. The library is intended for use only by the executable.
@@ -481,7 +481,7 @@ That said, the following may help:
 * Stack's imports are listed alphabetically, including `Stack.Prelude`, where
   applicable. The module names are left aligned, with space left for `qualified`
   where it is absent.
-* Stack's code is sufficiently stable that explict import lists can sensibly be
+* Stack's code is sufficiently stable that explicit import lists can sensibly be
   used. The exception is the import of `Stack.Prelude`. Not all modules have
   comprehensive explicit import lists.
 * Short explicit import lists follow the module name. Longer lists start on the

doc/maintainers/releases.md

@@ -67,7 +67,7 @@ Examples:
 
 4.  Check the copyright dates, and update if needed.
 
-5.  Check the backwards compatability section of `CONTRIBUTING.md` is up to
+5.  Check the backwards compatibility section of `CONTRIBUTING.md` is up to
     date.
 
 6.  Ensure CI matrices in docs (travis-complex, appveyor, azure) have current