Fix redundant Rails dependency, delegate to Devise

I removed any non-critical Rails-related dependencies and
aligned version requirements to Devise ones.

Fixes #3

Gemfile.lock

@@ -1,8 +1,10 @@
 PATH
   remote: .
   specs:
-    simple_token_authentication (0.0.1)
-      rails (~> 4.0.2)
+    simple_token_authentication (1.0.0.pre.beta.2)
+      actionmailer (>= 3.2.6, < 5)
+      activerecord (>= 3.2.6, < 5)
+      devise (~> 3.2.0)
 
 GEM
   remote: https://rubygems.org/
@@ -33,52 +35,43 @@ GEM
       tzinfo (~> 0.3.37)
     arel (4.0.1)
     atomic (1.1.14)
+    bcrypt-ruby (3.1.2)
     builder (3.1.4)
+    devise (3.2.2)
+      bcrypt-ruby (~> 3.0)
+      orm_adapter (~> 0.1)
+      railties (>= 3.2.6, < 5)
+      thread_safe (~> 0.1)
+      warden (~> 1.2.3)
     erubis (2.7.0)
-    hike (1.2.3)
     i18n (0.6.9)
     mail (2.5.4)
       mime-types (~> 1.16)
       treetop (~> 1.4.8)
     mime-types (1.25.1)
     minitest (4.7.5)
     multi_json (1.8.2)
+    orm_adapter (0.5.0)
     polyglot (0.3.3)
     rack (1.5.2)
     rack-test (0.6.2)
       rack (>= 1.0)
-    rails (4.0.2)
-      actionmailer (= 4.0.2)
-      actionpack (= 4.0.2)
-      activerecord (= 4.0.2)
-      activesupport (= 4.0.2)
-      bundler (>= 1.3.0, < 2.0)
-      railties (= 4.0.2)
-      sprockets-rails (~> 2.0.0)
     railties (4.0.2)
       actionpack (= 4.0.2)
       activesupport (= 4.0.2)
       rake (>= 0.8.7)
       thor (>= 0.18.1, < 2.0)
     rake (10.1.0)
-    sprockets (2.10.1)
-      hike (~> 1.2)
-      multi_json (~> 1.0)
-      rack (~> 1.0)
-      tilt (~> 1.1, != 1.3.0)
-    sprockets-rails (2.0.1)
-      actionpack (>= 3.0)
-      activesupport (>= 3.0)
-      sprockets (~> 2.8)
     sqlite3 (1.3.8)
     thor (0.18.1)
     thread_safe (0.1.3)
       atomic
-    tilt (1.4.1)
     treetop (1.4.15)
       polyglot
       polyglot (>= 0.3.1)
     tzinfo (0.3.38)
+    warden (1.2.3)
+      rack (>= 1.0)
 
 PLATFORMS
   ruby

simple_token_authentication.gemspec

@@ -16,7 +16,8 @@ Gem::Specification.new do |s|
   s.files = Dir["{app,config,db,lib}/**/*", "LICENSE", "Rakefile", "README.md"]
   s.test_files = Dir["test/**/*"]
 
-  s.add_dependency "rails", "~> 4.0.0"
+  s.add_dependency "activerecord", ">= 3.2.6", "< 5"
+  s.add_dependency "actionmailer", ">= 3.2.6", "< 5"
   s.add_dependency "devise", "~> 3.2.0"
 
   s.add_development_dependency "sqlite3"