Update Polyfill.nuspec

Author: SimonCropp

src/Polyfill/Polyfill.nuspec

@@ -15,7 +15,7 @@
   </metadata>
   <files>
     <file src="../icon.png" target="icon.png" />
-    <file src="../Split/**/*.cs" target="contentFiles/cs/"/>
+    <file src="..\Split\**\*.cs" target="contentFiles\cs\"/>
     <file src="Polyfill.targets" target="build"/>
     <file src="exclude.editorconfig" target=".editorconfig"/>
   </files>