Update repo's referenced NuGet version (#777)

Author: mthalman

eng/Versions.props

@@ -15,7 +15,7 @@
     <MicrosoftBuildVersion>15.6.82</MicrosoftBuildVersion>
     <MicrosoftBuildUtilitiesCoreVersion>$(MicrosoftBuildVersion)</MicrosoftBuildUtilitiesCoreVersion>
     <!-- NuGet dependencies -->
-    <NuGetPackagingVersion>6.4.0</NuGetPackagingVersion>
+    <NuGetPackagingVersion>6.7.0</NuGetPackagingVersion>
     <!-- Runtime dependencies -->
     <MicrosoftNETCoreILAsmVersion>6.0.0-preview.6.21352.12</MicrosoftNETCoreILAsmVersion>
     <MicrosoftNETCoreILDAsmVersion>6.0.0-preview.6.21352.12</MicrosoftNETCoreILDAsmVersion>