Ask before saving .travis.yml in encrypt* commands

[BanzaiMan]

Resolves #651.

[BanzaiMan]

$ bin/travis encrypt -a -C foo=bar


Overwrite the config file /Users/asari/Development/src/travis-ci/travis.rb/.travis.yml with the content below?

This reformats the existing file.

---
language: ruby
cache: bundler
os:
- linux
rvm:
- jruby
- 2.2.7
- 2.3.8
- 2.4.5
- 2.5.5
- 2.6.3
jobs:
  include:
  - os: osx
    rvm: 2.5.5
  - os: osx
    rvm: 2.6.3
  - stage: deploy
    if: branch = master and type = push
    os: linux
    rvm: 2.6.3
    deploy:
      provider: rubygems
      api_key:
        secure: KcBpkFaes74KGMm8X/rRA8e13+t3PmkefsAvOAR+iF4g1GyuLSPkP92Fb9vFfsXBph+qmFh5rNa2lIRf/3RXW6COxY7CMMaARxUfJOKE0rmIwF0qfKI+RZDh6abg92iYngunMZVN8WVft6Lv9ZTOYCWxr1Zs1Ll/Rl4PfvHNd1g=
      gem: travis
      true:
        repo: travis-ci/travis.rb
        ruby: 2.6.3
      edge: true
env:
  global:
    secure: cS7fkVbLAE83W7YDwxHju0TkuBEOQdXxBLYZdJ5qESU9GDEHvhDoTrsfShNCDaY+cg9LJFovjfBJqzGnci4Y1Wcv8XKneIUpqZYhp/pAIph4DdjNzRDUvx2sRho2ZkEdLCirAudepeweil/F/hyga59nrQsdiSIGCWFCh2/FKJQ=


(y/N)