Add '-s' ldflag and output size to travis tests

.travis.yml

@@ -13,6 +13,7 @@ install:
 script:
   - gofmt -l *.go */*.go */*/*.go
   - test -z "$(gofmt -l *.go */*.go */*/*.go)"
-  - go build ./...
+  - go build -ldflags "-s" ./...
+  - echo "binary size: $(stat --printf='%s' cmd/restic/restic)"
   - go test ./...
   - ./testsuite.sh