Refine `.travis.yml`
* Use `rake` instead of `minirake`.
* Remove `gperf` configuration.
Execution time seems to be reduced by about 15%.
@@ -9,11 +9,6 @@ matrix:
- os: osx
osx_image: xcode7.1
-addons:
- apt:
- packages:
- - gperf
-
env:
- MRUBY_CONFIG=travis_config.rb
-script: "./minirake -j4 all test"
+script: "rake -m -E '$stdout.sync=true' all test"
