encoding/protobuf: don't map google.protobuf types

(at least not yet)

Issue #5

Change-Id: If8430cf8ec9bb376bcf0c69ec385f1f0d066c4e6
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/2374
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
diff --git a/encoding/protobuf/testdata/client_config.proto.out.cue b/encoding/protobuf/testdata/client_config.proto.out.cue
index 66ec87a..fc7f747 100644
--- a/encoding/protobuf/testdata/client_config.proto.out.cue
+++ b/encoding/protobuf/testdata/client_config.proto.out.cue
@@ -21,8 +21,8 @@
 package client
 
 import (
+	"github.com/golang/protobuf/ptypes/duration"
 	"istio.io/api/mixer/v1"
-	"time"
 )
 
 //  Specifies the behavior when the client is unable to connect to Mixer.
@@ -36,10 +36,10 @@
 
 	//  Base time to wait between retries.  Will be adjusted by exponential
 	//  backoff and jitter.
-	baseRetryWait?: time.Duration @protobuf(3,type=google.protobuf.Duration,name=base_retry_wait)
+	baseRetryWait?: duration.Duration @protobuf(3,type=google.protobuf.Duration,name=base_retry_wait)
 
 	//  Max time to wait between retries.
-	maxRetryWait?: time.Duration @protobuf(4,type=google.protobuf.Duration,name=max_retry_wait)
+	maxRetryWait?: duration.Duration @protobuf(4,type=google.protobuf.Duration,name=max_retry_wait)
 }
 
 //  Example of single-value enum.
@@ -108,7 +108,7 @@
 
 	//  Specify refresh interval to write Mixer client statistics to Envoy share
 	//  memory. If not specified, the interval is 10 seconds.
-	statsUpdateInterval?: time.Duration @protobuf(5,type=google.protobuf.Duration,name=stats_update_interval)
+	statsUpdateInterval?: duration.Duration @protobuf(5,type=google.protobuf.Duration,name=stats_update_interval)
 
 	//  Name of the cluster that will forward check calls to a pool of mixer
 	//  servers. Defaults to "mixer_server". By using different names for
@@ -183,5 +183,5 @@
 	//  Specify report interval to send periodical reports for long TCP
 	//  connections. If not specified, the interval is 10 seconds. This interval
 	//  should not be less than 1 second, otherwise it will be reset to 1 second.
-	reportInterval?: time.Duration @protobuf(6,type=google.protobuf.Duration,name=report_interval)
+	reportInterval?: duration.Duration @protobuf(6,type=google.protobuf.Duration,name=report_interval)
 }