locking bundler version to prevent build issues

Gemfile

@@ -4,6 +4,7 @@
 source 'https://rubygems.org'
 
 group :development, :test do
+  gem 'bundler', '1.17.1'
   gem 'jekyll', '~> 3.9.0'
   gem 'jekyll-redirect-from', '~> 0.13.0'
   gem 'jekyll-sitemap', '~> 1.2.0'

Gemfile.lock

@@ -73,6 +73,7 @@ PLATFORMS
   ruby
 
 DEPENDENCIES
+  bundler (= 1.17.1)
   jekyll (~> 3.9.0)
   jekyll-last-modified-at (~> 1.0)
   jekyll-redirect-from (~> 0.13.0)
@@ -83,4 +84,4 @@ DEPENDENCIES
   redcarpet (~> 3.5.1)
 
 BUNDLED WITH
-   1.17.3
+   1.17.1