Fix content type detection for JSON files.

lib/carrierwave/sanitized_file.rb

@@ -315,7 +315,7 @@ module CarrierWave
 
       if type.nil?
         type = Marcel::Magic.by_path(path).try(:type)
-        type = 'invalid/invalid' unless type.nil? || type.start_with?('text/')
+        type = 'invalid/invalid' unless type.nil? || type.start_with?('text/') || type.start_with?('application/json')
       end
 
       type

spec/fixtures/bork.json

@@ -0,0 +1,3 @@
+{
+  "bork": "bork"
+}

spec/sanitized_file_spec.rb

@@ -264,6 +264,16 @@ describe CarrierWave::SanitizedFile do
       expect(sanitized_file.content_type).to eq 'text/plain'
     end
 
+    it "returns valid content type on JSON file (which is a text file in disguise)" do
+      file = File.open(file_path('bork.json'))
+
+      sanitized_file = CarrierWave::SanitizedFile.new(file)
+
+      expect { sanitized_file.content_type }.not_to raise_error
+
+      expect(sanitized_file.content_type).to eq 'application/json'
+    end
+
     it "returns missing content type with unknown extension" do
       file = File.open(file_path('bork.ABCDE'))