travis, intall exact bundler version
travis, intall exact bundler version

Trying to address the following error on Travis:

**Error:**
```
$ bundle install --jobs=3 --retry=3 --deployment
Traceback (most recent call last):
	4: from /home/travis/.rvm/gems/ruby-2.7.1/bin/ruby_executable_hooks:24:in `<main>'
	3: from /home/travis/.rvm/gems/ruby-2.7.1/bin/ruby_executable_hooks:24:in `eval'
	2: from /home/travis/.rvm/gems/ruby-2.7.1/bin/bundle:23:in `<main>'
	1: from /home/travis/.rvm/rubies/ruby-2.7.1/lib/ruby/2.7.0/rubygems.rb:294:in `activate_bin_path'
/home/travis/.rvm/rubies/ruby-2.7.1/lib/ruby/2.7.0/rubygems.rb:275:in `find_spec_for_exe': Could not find 'bundler' (1.17.2) required by your /home/travis/build/senny/sablon/Gemfile.lock. (Gem::GemNotFoundException)
To update to the latest version installed on your system, run `bundle update --bundler`.
To install the missing version, run `gem install bundler:1.17.2`
The command "eval bundle install --jobs=3 --retry=3 --deployment " failed. Retrying, 2 of 3.
```

fullfabric/sablon,senny/sablon