Travis Tweaking

* Apparently mono and xbuild don't like .NET 4.5.2
/usr/lib/mono/xbuild/12.0/bin/Microsoft.Common.targets:  warning : TargetFrameworkVersion 'v4.5.2' not supported by this toolset (ToolsVersion: 12.0).
* Reverting to v4.5

Author: McNeight

ICSharpCode.SharpZipLib/ICSharpCode.SharpZipLib.csproj

@@ -17,7 +17,7 @@
     <PreBuildEvent />
     <PostBuildEvent />
     <DocumentationFile>..\bin\ICSharpCode.SharpZipLib.xml</DocumentationFile>
-    <TargetFrameworkVersion>v4.5.2</TargetFrameworkVersion>
+    <TargetFrameworkVersion>v4.5</TargetFrameworkVersion>
     <TargetFrameworkProfile />
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">