Add missing require and remove unnecessary requires

lib/danger/plugin_support/gems_resolver.rb

@@ -1,3 +1,5 @@
+require "bundler"
+
 module Danger
   class GemsResolver
     def initialize(gem_names)

lib/danger/plugin_support/plugin_file_resolver.rb

@@ -1,6 +1,4 @@
-require "bundler"
-require "pathname"
-require "fileutils"
+require "danger/plugin_support/gems_resolver"
 
 module Danger
   class PluginFileResolver

spec/lib/danger/plugin_support/plugin_file_resolver_spec.rb

@@ -0,0 +1,15 @@
+require "lib/danger/plugin_support/plugin_file_resolver"
+
+RSpec.describe Danger::PluginFileResolver do
+  describe "#resolve" do
+    context "Given list of gems" do
+      it "resolves for gems" do
+        resolver = Danger::PluginFileResolver.new(["danger", "rails"])
+
+        expect(Danger::GemsResolver).to receive_message_chain(:new, :call)
+
+        resolver.resolve
+      end
+    end
+  end
+end