Fix Rubocop violations

Author: infertux

.rubocop.yml

@@ -1,4 +1,4 @@
-require:
+plugins:
   - rubocop-rake
   - rubocop-rspec
 

lib/bashcov/runner.rb

@@ -34,8 +34,8 @@ def run
       options[fd] = fd # bind FDs to the child process
 
       if Bashcov.options.mute
-        options[:out] = "/dev/null"
-        options[:err] = "/dev/null"
+        options[:out] = File::NULL
+        options[:err] = File::NULL
       end
 
       env =

spec/bashcov/runner_spec.rb

@@ -231,7 +231,7 @@
       it "omits files matching one or more SimpleCov filters from the results hash" do
         runner.run
         result = runner.result
-        expect(result.keys).to match_array((expected_coverage.keys - expected_omitted.values.flatten))
+        expect(result.keys).to match_array(expected_coverage.keys - expected_omitted.values.flatten)
       end
     end
   end