Fixed missing --configuration flag in build script

Author: Daniel James

.travis.yml

@@ -7,7 +7,7 @@ dotnet: 2.0.0
 
 script:
   - dotnet restore
-  - dotnet build
+  - dotnet build --configuration Release
   - "if [[ $TRAVIS_PULL_REQUEST == 'false' && $TRAVIS_TAG ]]; then 
   dotnet pack . --configuration Release /p:Version=$TRAVIS_TAG;
   nuget push ./bin/Release/*.nupkg -ApiKey $NUGET_API_KEY;