Rename bcrypt-ruby gem to bcrypt as per deprecation warning

See bcrypt-ruby/bcrypt-ruby#86

Test plan:
* specs pass

Change-Id: Icb8aaaa332a6b3d9be82fb3ad76e234b66801480
Reviewed-on: https://gerrit.instructure.com/93999
Reviewed-by: Derek Bender <djbender@instructure.com>
Reviewed-by: Shahbaz Javeed <sjaveed@instructure.com>
Tested-by: Jenkins
Product-Review: Neil Gupta <ngupta@instructure.com>
QA-Review: Neil Gupta <ngupta@instructure.com>

Gemfile.d/app.rb

@@ -36,7 +36,7 @@
 gem 'barby', '0.5.0', require: false
   gem 'rqrcode', '0.4.2', require: false
   gem 'chunky_png', '1.3.0', require: false
-gem 'bcrypt-ruby', '3.1.5'
+gem 'bcrypt', '3.1.11'
 gem 'canvas_connect', '0.3.10'
   gem 'adobe_connect', '1.0.4', require: false
 gem 'canvas_webex', '0.17'