Update dependencies

Among others, this updates minio-go, so that the new "eu-west-3" zone
for AWS is supported.

vendor/cloud.google.com/go/internal/snipdoc/sample-makefile

@@ -0,0 +1,16 @@
+# Build doc.go from template and snippets.
+
+SHELL=/bin/bash
+
+../doc.go: build doc-snippets.go doc.template snipdoc.awk
+	@tmp=$$(mktemp) && \
+	awk -f snipdoc.awk doc-snippets.go doc.template > $$tmp && \
+	chmod +w $@ && \
+	mv $$tmp $@ && \
+	chmod -w $@
+	@echo "wrote $@"
+
+.PHONY: build
+
+build:
+	go build doc-snippets.go