Check gofmt in travis tests

.travis.gofmt.sh

@@ -0,0 +1,8 @@
+#!/bin/bash
+
+result="$(gofmt -s -l .)"
+if [ -n "$result" ]; then
+  echo "Go code is not formatted, run 'gofmt -s -w .'" >&2
+  echo "$result"
+  exit 1
+fi

.travis.yml

@@ -8,4 +8,5 @@ install:
   - go get golang.org/x/tools/cmd/cover
 script:
   - ./.test-coverage travis-ci
+  - ./.travis.gofmt.sh
   - go install github.com/FreifunkBremen/yanic