Make "Two-factor" casing consistent throughout the application

CHANGELOG

@@ -91,7 +91,7 @@ v 8.4.0
   - Show 'All' tab by default in the builds page
   - Add Open Graph and Twitter Card data to all pages
   - Fix API project lookups when querying with a namespace with dots (Stan Hu)
-  - Enable forcing Two-Factor authentication sitewide, with optional grace period
+  - Enable forcing Two-factor authentication sitewide, with optional grace period
   - Import GitHub Pull Requests into GitLab
   - Change single user API endpoint to return more detailed data (Michael Potthoff)
   - Update version check images to use SVG

app/views/admin/application_settings/_form.html.haml

@@ -105,14 +105,14 @@
             = f.check_box :signin_enabled
             Sign-in enabled
     .form-group
-      = f.label :two_factor_authentication, 'Two-Factor authentication', class: 'control-label col-sm-2'
+      = f.label :two_factor_authentication, 'Two-factor authentication', class: 'control-label col-sm-2'
       .col-sm-10
         .checkbox
           = f.label :require_two_factor_authentication do
             = f.check_box :require_two_factor_authentication
-            Require all users to setup Two-Factor authentication
+            Require all users to setup Two-factor authentication
     .form-group
-      = f.label :two_factor_authentication, 'Two-Factor grace period (hours)', class: 'control-label col-sm-2'
+      = f.label :two_factor_authentication, 'Two-factor grace period (hours)', class: 'control-label col-sm-2'
       .col-sm-10
         = f.number_field :two_factor_grace_period, min: 0, class: 'form-control', placeholder: '0'
         .help-block Amount of time (in hours) that users are allowed to skip forced configuration of two-factor authentication

app/views/profiles/two_factor_auths/new.html.haml

 - page_title 'Two-factor Authentication', 'Account'
 
-%h2.page-title Two-Factor Authentication (2FA)
+%h2.page-title Two-factor Authentication (2FA)
 %p
   Download the Google Authenticator application from App Store for iOS or Google
   Play for Android and scan this code.

doc/security/README.md

@@ -7,4 +7,4 @@
 - [Reset your root password](reset_root_password.md)
 - [User File Uploads](user_file_uploads.md)
 - [How we manage the CRIME vulnerability](crime_vulnerability.md)
-- [Enforce Two-Factor authentication](two_factor_authentication.md)
+- [Enforce Two-factor authentication](two_factor_authentication.md)