remove explicit bootstrap-sass dependency

To pave the way for bootstrap 4 support. App needs to decide whether it wants bootstrap 3 or 4, and include the proper dependency itself. Browse-everything including the bootstrap-sass dependency in it's gemspec prevented apps from using bootstrap4, which is delivered via a separate gem called just , as they would conflict.

README.md

@@ -78,7 +78,9 @@ If you prefer not to use the generator, or need info on how to set up providers
 
 ### Include the CSS and JavaScript
 
-If you don't already have `@import 'bootstrap-sprockets'` and `@import 'bootstrap'` in your `application.scss`, add them. Somewhere after those lines, add  `@import "browse_everything";` to your application.scss.
+Browse-everything depends on bootstrap. If your app does not already have (Bootstrap3) [bootstrap-sass](https://github.com/twbs/bootstrap-sass) in it's dependencies, you should add it to your Gemfile.
+
+If you don't already have `@import 'bootstrap-sprockets'` and `@import 'bootstrap'` in your `application.scss` (per bootstrap-sass installation instructions), add them. Somewhere after those lines, add  `@import "browse_everything";` to your application.scss.
 
 In `app/assets/javascripts/application.js` include jquery and the BrowseEverything
 

browse-everything.gemspec

@@ -21,7 +21,6 @@ Gem::Specification.new do |spec|
 
   spec.add_dependency 'addressable', '~> 2.5'
   spec.add_dependency 'aws-sdk-s3'
-  spec.add_dependency 'bootstrap-sass', '~> 3.2'
   spec.add_dependency 'dropbox_api', '>= 0.1.10'
   spec.add_dependency 'google-api-client', '~> 0.23'
   spec.add_dependency 'google_drive', '~> 2.1'

lib/browse-everything.rb

@@ -1,4 +1,3 @@
 # frozen_string_literal: true
 
-require 'bootstrap-sass'
 require 'browse_everything'

spec/test_app_templates/Gemfile.extra

@@ -1,2 +1,4 @@
 gem 'jquery-rails'
 gem 'puma-rails'
+# bootstrap3
+gem "bootstrap-sass"