Add extension to filename check in targets file

Doesn't hurt to add it!

Author: bording

LibGit2Sharp/NativeDllName.targets

@@ -14,7 +14,7 @@
   <Target Name="GenerateNativeDllNameCs"
           Inputs="@(EmbeddedResource)"
           Outputs="$(NativeDllNamePath)">
-    <GenerateNativeDllNameTask InputHashFile="@(EmbeddedResource)" Condition=" '%(Filename)' == 'libgit2_hash' " OutputFile="$(NativeDllNamePath)" />
+    <GenerateNativeDllNameTask InputHashFile="@(EmbeddedResource)" Condition=" '%(Filename)%(Extension)' == 'libgit2_hash.txt' " OutputFile="$(NativeDllNamePath)" />
   </Target>
 
  <Target Name="CleanNativeDllNameCs">