Speed up Travis build

Modify to use standard mode and directory cache for Travis CI build.

Closes gh-7043

Author: kazuki43zoo

.travis.yml

@@ -5,7 +5,10 @@ services:
   - mongodb
   - redis
   - cassandra
-sudo: false
+sudo: required
+cache:
+  directories:
+    - $HOME/.m2
 install: true
 before_script: travis_wait 45 ./mvnw install -q -U -DskipTests=true -Pfast -Dmaven.test.redirectTestOutputToFile=true
 script: ./mvnw install -q -nsu -Dmaven.test.redirectTestOutputToFile=true -P '!integration'