Fix data-uri with mime type that has `.` in it

Fixes #1550

lib/paperclip/io_adapters/data_uri_adapter.rb

 module Paperclip
   class DataUriAdapter < StringioAdapter
 
-    REGEXP = /\Adata:([-\w]+\/[-\w\+]+)?;base64,(.*)/m
+    REGEXP = /\Adata:([-\w]+\/[-\w\+\.]+)?;base64,(.*)/m
 
     def initialize(target_uri)
       super(extract_target(target_uri))

spec/paperclip/io_adapters/data_uri_adapter_spec.rb

@@ -12,6 +12,11 @@ describe Paperclip::DataUriAdapter do
     assert_equal Paperclip::DataUriAdapter, adapter.class
   end
 
+  it 'alows mime type that has dot in it' do
+    adapter = Paperclip.io_adapters.for("data:image/vnd.microsoft.icon;base64,#{original_base64_content}")
+    assert_equal Paperclip::DataUriAdapter, adapter.class
+  end
+
   context "a new instance" do
     before do
       @contents = "data:image/png;base64,#{original_base64_content}"