Project fix

Author: dwarfland

Source/Swift.Shared.projitems

@@ -29,7 +29,9 @@
     <Compile Include="$(MSBuildThisFileDirectory)Set.swift">
       <VirtualFolder>Collection Types</VirtualFolder>
     </Compile>
-    <Compile Include="$(MSBuildThisFileDirectory)String_Extensions.swift" />
+    <Compile Include="$(MSBuildThisFileDirectory)String_Extensions.swift">
+      <VirtualFolder>String</VirtualFolder>
+    </Compile>
     <Compile Include="$(MSBuildThisFileDirectory)String.swift">
       <VirtualFolder>String</VirtualFolder>
     </Compile>