Remove this so that Xamarin Studio can install the NuGet

nuget/SkiaSharp.nuspec

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <package>
-  <metadata minClientVersion="3.5">
+  <metadata>
     <id>SkiaSharp</id>
     <title>SkiaSharp</title>
     <version>1.57.1</version>