codec: travis: add test for GOARCH=386

.travis.yml

@@ -9,6 +9,7 @@ go:
     - 1.12.x
     - tip
 script:
+    - GOARCH=386 go test -tags "alltests" -run Suite -coverprofile coverage.386.txt github.com/ugorji/go/codec
     - go test -tags "alltests" -run Suite -coverprofile coverage.txt github.com/ugorji/go/codec
     - go test -tags "alltests safe" -run Suite -coverprofile coverage.safe.txt github.com/ugorji/go/codec
     - go test -tags "alltests codecgen" -run Suite -coverprofile coverage.codecgen.txt github.com/ugorji/go/codec