Add npm-shrinkwrap.json to generated files (#3048)

This file is generated by the `npm shrinkwrap` command. It's large,
generated, and has a noisey diff. One similar file, php composer lock
files, is already ignored.

Closes https://github.com/github/linguist/issues/3045

lib/linguist/generated.rb

@@ -56,6 +56,7 @@ module Linguist
       generated_net_specflow_feature_file? ||
       composer_lock? ||
       node_modules? ||
+      npm_shrinkwrap? ||
       godeps? ||
       generated_by_zephir? ||
       minified_files? ||
@@ -303,6 +304,13 @@ module Linguist
       !!name.match(/node_modules\//)
     end
 
+    # Internal: Is the blob a generated npm shrinkwrap file.
+    #
+    # Returns true or false.
+    def npm_shrinkwrap?
+      !!name.match(/npm-shrinkwrap\.json/)
+    end
+
     # Internal: Is the blob part of Godeps/,
     # which are not meant for humans in pull requests.
     #

test/test_generated.rb

@@ -51,6 +51,9 @@ class TestGenerated < Minitest::Test
     # Node modules
     generated_sample_without_loading_data("Dummy/node_modules/foo.js")
 
+    # npm shrinkwrap file
+    generated_sample_without_loading_data("Dummy/npm-shrinkwrap.json")
+
     # Godep saved dependencies
     generated_sample_without_loading_data("Godeps/Godeps.json")
     generated_sample_without_loading_data("Godeps/_workspace/src/github.com/kr/s3/sign.go")