Update building.md (#6635)

Fix invalid yaml in building docs

Author: jimschubert

docs/building.md

@@ -43,7 +43,7 @@ Once built, `run-in-docker.sh` will act as an executable for openapi-generator-c
 ```bash
 ./run-in-docker.sh help # Executes 'help' command for openapi-generator-cli
 ./run-in-docker.sh list # Executes 'list' command for openapi-generator-cli
-./run-in-docker.sh /gen/bin/generate-samples.sh /gen/bin/configs/go-petstore.yaml/  # Builds the Go client
+./run-in-docker.sh /gen/bin/generate-samples.sh /gen/bin/configs/go-petstore.yaml  # Builds the Go client
 ./run-in-docker.sh generate -i modules/openapi-generator/src/test/resources/2_0/petstore.yaml \
     -g go -o /gen/out/go-petstore -DpackageName=petstore # generates go client, outputs locally to ./out/go-petstore
 ```