Add appraisal for Rails 5.2 rc

Author: swrobel

.travis.yml

@@ -10,6 +10,7 @@ rvm:
 #  - rbx
 
 gemfile:
+  - gemfiles/activerecord_5.2.gemfile
   - gemfiles/activerecord_5.1.gemfile
   - gemfiles/activerecord_5.0.gemfile
   - gemfiles/activerecord_4.2.gemfile

gemfiles/activerecord_5.2.gemfile

@@ -0,0 +1,19 @@
+# This file was generated by Appraisal
+
+source "https://rubygems.org"
+
+gem "rails", '~> 5.2.0.rc2'
+
+platforms :ruby, :rbx do
+  gem "mysql2", '~> 0.4.10'
+  gem "pg"
+  gem "sqlite3"
+end
+
+platforms :jruby do
+  gem "activerecord-jdbcmysql-adapter"
+  gem "activerecord-jdbcpostgresql-adapter"
+  gem "activerecord-jdbcsqlite3-adapter"
+end
+
+gemspec :path => "../"