Trivial func and var naming changes (golint)

This makes to code at little more idiomatic and fixes:

server_metrics.go:140:6: func streamRpcType should be streamRPCType
server_test.go:97:6: range var testId should be testID

server_metrics.go

@@ -117,7 +117,7 @@ func (m *ServerMetrics) UnaryServerInterceptor() func(ctx context.Context, req i
 // StreamServerInterceptor is a gRPC server-side interceptor that provides Prometheus monitoring for Streaming RPCs.
 func (m *ServerMetrics) StreamServerInterceptor() func(srv interface{}, ss grpc.ServerStream, info *grpc.StreamServerInfo, handler grpc.StreamHandler) error {
 	return func(srv interface{}, ss grpc.ServerStream, info *grpc.StreamServerInfo, handler grpc.StreamHandler) error {
-		monitor := newServerReporter(m, streamRpcType(info), info.FullMethod)
+		monitor := newServerReporter(m, streamRPCType(info), info.FullMethod)
 		err := handler(srv, &monitoredServerStream{ss, monitor})
 		st, _ := status.FromError(err)
 		monitor.Handled(st.Code())
@@ -137,7 +137,7 @@ func (m *ServerMetrics) InitializeMetrics(server *grpc.Server) {
 	}
 }
 
-func streamRpcType(info *grpc.StreamServerInfo) grpcType {
+func streamRPCType(info *grpc.StreamServerInfo) grpcType {
 	if info.IsClientStream && !info.IsServerStream {
 		return ClientStream
 	} else if !info.IsClientStream && info.IsServerStream {

server_test.go

@@ -94,7 +94,7 @@ func (s *ServerInterceptorTestSuite) TearDownSuite() {
 }
 
 func (s *ServerInterceptorTestSuite) TestRegisterPresetsStuff() {
-	for testId, testCase := range []struct {
+	for testID, testCase := range []struct {
 		metricName     string
 		existingLabels []string
 	}{
@@ -110,7 +110,7 @@ func (s *ServerInterceptorTestSuite) TestRegisterPresetsStuff() {
 		{"grpc_server_handled_total", []string{"mwitkow.testproto.TestService", "PingEmpty", "unary", "ResourceExhausted"}},
 	} {
 		lineCount := len(fetchPrometheusLines(s.T(), testCase.metricName, testCase.existingLabels...))
-		assert.NotEqual(s.T(), 0, lineCount, "metrics must exist for test case %d", testId)
+		assert.NotEqual(s.T(), 0, lineCount, "metrics must exist for test case %d", testID)
 	}
 }