fix: remove duplicated mount option (#12)

Works for docker because docker allows duplicated mount
volumes, but podman doesn't:

- containers/podman#4217

Makefile

@@ -9,7 +9,7 @@ DOCKER_RUN_FLAGS += --rm
 DOCKER_RUN_FLAGS += -v ${PWD}:/src
 
 DOCKER_TOOLS_REPO   = mineiros/golang-tools
-DOCKER_TOOLS_FLAGS += -v $(PWD):/src $(DOCKER_TOOLS_REPO)
+DOCKER_TOOLS_FLAGS += $(DOCKER_TOOLS_REPO)
 
 DOCKER_FLAGS   += ${DOCKER_RUN_FLAGS}
 DOCKER_RUN_CMD  = docker run ${DOCKER_FLAGS}