Add tips when unittest error

Author: reyoung

paddle/scripts/travis/precommit.sh

@@ -1,8 +1,17 @@
 #!/bin/bash
+function abort(){
+    echo "Your commit not fit PaddlePaddle code style" 1>&2
+    echo "Please use pre-commit scripts to auto-format your code" 1>&2
+    exit 1
+}
+
+trap 'abort' 0
 set -e
 source common.sh
 cd ..
 export PATH=/usr/bin:$PATH
 pre-commit install
 clang-format --version
 pre-commit run -a
+
+trap : 0