Fix inconsistent naming

CONTRIBUTING.md

@@ -1,6 +1,6 @@
-## Contributing to the Guidelines Support Library
+## Contributing to the Guideline Support Library
 
-The Guidelines Support Library (GSL) contains functions and types that are suggested for use by the
+The Guideline Support Library (GSL) contains functions and types that are suggested for use by the
 [C++ Core Guidelines](https://github.com/isocpp/CppCoreGuidelines). GSL design changes are made only as a result of modifications to the Guidelines. 
 
 GSL is accepting contributions that improve or refine any of the types in this library as well as ports to other platforms. Changes should have an issue 

README.md

@@ -1,6 +1,6 @@
-# GSL: Guidelines Support Library [![Build Status](https://travis-ci.org/Microsoft/GSL.svg?branch=master)](https://travis-ci.org/Microsoft/GSL) [![Build status](https://ci.appveyor.com/api/projects/status/github/Microsoft/GSL?svg=true)](https://ci.appveyor.com/project/neilmacintosh/GSL)
+# GSL: Guideline Support Library [![Build Status](https://travis-ci.org/Microsoft/GSL.svg?branch=master)](https://travis-ci.org/Microsoft/GSL) [![Build status](https://ci.appveyor.com/api/projects/status/github/Microsoft/GSL?svg=true)](https://ci.appveyor.com/project/neilmacintosh/GSL)
 
-The Guidelines Support Library (GSL) contains functions and types that are suggested for use by the
+The Guideline Support Library (GSL) contains functions and types that are suggested for use by the
 [C++ Core Guidelines](https://github.com/isocpp/CppCoreGuidelines) maintained by the [Standard C++ Foundation](https://isocpp.org).
 This repo contains Microsoft's implementation of GSL.