Update nuget-package.props

Bump nuget version to 0.15

Author: shawncal

dotnet/nuget/nuget-package.props

@@ -1,7 +1,7 @@
 <Project>
   <PropertyGroup>
     <!-- Central version prefix - applies to all nuget packages. -->
-    <Version>0.14</Version>
+    <Version>0.15</Version>
 
     <Configurations>Debug;Release;Publish</Configurations>
     <IsPackable>true</IsPackable>
@@ -49,4 +49,4 @@
   <PropertyGroup Condition=" '$(Configuration)' == 'Release' ">
     <GeneratePackageOnBuild>true</GeneratePackageOnBuild>
   </PropertyGroup>
-</Project>
+</Project>