touch exes after running build command

The executables have dependencies that are not apparent to `go build`;
notably the build container. If Go doesn't see anything is out of date
then it will do nothing, hence touch the file so next time we run
`make` it is up to date.

Makefile

@@ -179,6 +179,7 @@ exes $(EXES) tests lint: $(BUILD_UPTODATE)
 		-v $(shell pwd)/.pkg:/go/pkg \
 		-e GOARCH=$(ARCH) -e CGO_ENABLED=1 -e GOOS=linux -e CIRCLECI -e CIRCLE_BUILD_NUM -e CIRCLE_NODE_TOTAL -e CIRCLE_NODE_INDEX -e COVERDIR -e SLOW -e DEBUG \
 		$(BUILD_IMAGE) COVERAGE=$(COVERAGE) WEAVE_VERSION=$(WEAVE_VERSION) CC=$(CC) QEMUARCH=$(QEMUARCH) CGO_LDFLAGS=$(CGO_LDFLAGS) $@
+	touch $@
 
 else