FIX: Build fails when the user directory has a space. (#56)

* Fix mellinoe/veldrid#70

* &$&$&$&$&$

src/ShaderGen.Build/ShaderGen.targets

@@ -32,7 +32,7 @@
       <_SGContinueOnError Condition="'$(DesignTimeBuild)' == 'true'">true</_SGContinueOnError>
     </PropertyGroup>
 
-    <Exec Command="dotnet $(_SGExePath) $(_SGArgs)"
+    <Exec Command="dotnet &quot;$(_SGExePath)&quot; $(_SGArgs)"
           WorkingDirectory="$(MSBuildProjectDirectory)"
           StandardOutputImportance="high"
           ContinueOnError="$(_SGContinueOnError)" />
@@ -63,4 +63,4 @@
     </ItemGroup>
   </Target>
 
-</Project>
+</Project>