Make Code Analysis (and build) work on en-[!US]

This was done in other project files in #426.

Before this PR, I get the following build errors:

```
Build FAILED.

       "c:\My\repo\octokit.net\Octokit.sln" (Build target) (1) ->
       "c:\My\repo\octokit.net\Octokit\Octokit-Portable.csproj" (default target) (9) ->
       (RunCodeAnalysis target) ->
         MSBUILD : error CA1704: Microsoft.Naming : Correct the spelling of 'Catalog' in member name 'Language.GettextCatalog' or remove it entirely if it represents any sort of Hungarian notation. [c:\My\repo\octokit.net\Octokit\Octokit-Portable.csproj]
         MSBUILD : error CA1704: Microsoft.Naming : Correct the spelling of 'Prolog' in member name 'Language.Prolog' or remove it entirely if it represents any sort of Hungarian notation. [c:\My\repo\octokit.net\Octokit\Octokit-Portable.csproj]
         MSBUILD : error : Code Analysis detected errors.  See Code Analysis results window or log file for details. [c:\My\repo\octokit.net\Octokit\Octokit-Portable.csproj]
```
Merge pull request #446 from adamchester/patch-1

Make Code Analysis (and build) work on en-[!US]