Fix brittle test (#1127)

Update brittle test to handle new standard command.

Instead of locking standard to a specific version to avoid test
failures, we update the test to account for the new command provided by
a recent [release][1]

[1]: https://github.com/standardrb/standard/releases/tag/v1.26.0

spec/suspenders/generators/lint_generator_spec.rb

@@ -20,9 +20,10 @@
         # rake task works and we don't need to fake it
         rake_output = `rake -T`
 
-        expect(rake_output.lines.size).to eq 2
+        expect(rake_output.lines.size).to eq 3
         expect(rake_output.lines[0]).to start_with("rake standard")
         expect(rake_output.lines[1]).to start_with("rake standard:fix")
+        expect(rake_output.lines[2]).to start_with("rake standard:fix_unsafely")
       end
     end
   end