Update Directory.build.props

Author: ChrisPulman

src/Directory.build.props

@@ -36,7 +36,7 @@
     <XunitVersion>2.6.1</XunitVersion>
   </PropertyGroup>
   <PropertyGroup Condition="$(IsTestProject) != 'true'">
-    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+    <TreatWarningsAsErrors>false</TreatWarningsAsErrors>
   </PropertyGroup>
 
   <!-- MonoAndroid doesn't seem to want to allow debugging for maintainers -->