Update dependencies, use ruby 2.5.3 for testing

.travis.yml

@@ -1,6 +1,4 @@
 language: ruby
 rvm:
-  - 2.3.0
-before_install:
-  - gem install bundler
+  - 2.5.3
 script: rake ci

Gemfile

@@ -1,5 +1,5 @@
 source 'https://rubygems.org'
 
-ruby '2.3.0'
+ruby '2.5.3'
 gem 'rake'
 gem 'vim-flavor', '~> 1.1'

Gemfile.lock

@@ -18,7 +18,7 @@ DEPENDENCIES
   vim-flavor (~> 1.1)
 
 RUBY VERSION
-   ruby 2.3.0p0
+   ruby 2.5.3p105
 
 BUNDLED WITH
-   1.13.6
+   2.0.1