Update Polyfill.targets

Author: SimonCropp

src/Polyfill/Polyfill.targets

@@ -12,7 +12,7 @@
   </PropertyGroup>
   <PropertyGroup Condition="$(PolyNullability) == 'true' ">
     <DefineConstants>$(DefineConstants);PolyNullability</DefineConstants>
-  </PropertyGroup>  
+  </PropertyGroup>
   <PropertyGroup Condition="$(LowerFramework.StartsWith('netcoreapp2'))">
     <DefineConstants>$(DefineConstants);NETCOREAPP2X</DefineConstants>
   </PropertyGroup>