Update dockerfile

Author: stevejgordon

.ci/DockerFile

@@ -21,6 +21,7 @@ COPY ./tests/*.Build.props  ./tests/
 # Copy the main source project files
 COPY src/*/*.?sproj ./src/
 COPY tests/*/*.?sproj ./tests/
+COPY benchmarks/*/*.?sproj ./benchmarks/
 
 # this puts the project files back into original location since COPY flattens
 RUN for file in $(find . -name "*.?sproj"); do echo mkdir -p $(dirname $file)/$(basename ${file%.*})/ && echo mv $file $(dirname $file)/$(basename ${file%.*})/; done