reduce timeout for tests to 5m (7m for testrace) (#1635)

diff --git a/Makefile b/Makefile
index 39606b5..c445343 100644
--- a/Makefile
+++ b/Makefile
@@ -23,10 +23,10 @@
 	go generate google.golang.org/grpc/...
 
 test: testdeps
-	go test -cpu 1,4 google.golang.org/grpc/...
+	go test -cpu 1,4 -timeout 5m google.golang.org/grpc/...
 
 testrace: testdeps
-	go test -race -cpu 1,4 google.golang.org/grpc/...
+	go test -race -cpu 1,4 -timeout 7m google.golang.org/grpc/...
 
 clean:
 	go clean -i google.golang.org/grpc/...