Bump version to 0.1.21-pre1 (#291)

* build other packages too

* set nupkg version to 0.1.21-pre1

Author: jtattermusch

build/version.props

@@ -1,6 +1,6 @@
 <Project>
   <PropertyGroup>
     <!-- version of all grpc-dotnet packages -->
-    <GrpcDotnetVersion>0.1.21-dev</GrpcDotnetVersion>
+    <GrpcDotnetVersion>0.1.21-pre1</GrpcDotnetVersion>
   </PropertyGroup>
 </Project>

kokoro/build_nuget.sh

@@ -30,3 +30,6 @@ mkdir -p artifacts
 build/expand_dev_version.sh
 
 (cd src/Grpc.AspNetCore.Server && dotnet pack --configuration Release --output ../../artifacts)
+(cd src/Grpc.AspNetCore.Server.ClientFactory && dotnet pack --configuration Release --output ../../artifacts)
+(cd src/Grpc.Net.Client && dotnet pack --configuration Release --output ../../artifacts)
+(cd src/Grpc.Net.ClientFactory && dotnet pack --configuration Release --output ../../artifacts)