Fixes typo in lesson 1.3 alert steps modal

I noticed there's a typo in the 1.3 alert modal.  If you follow the
directions to the T, it won't pass because it commits to the wrong
branch.

It needs to say make a new branch called `bugFix`,
then `git checkout bugFix`, then commit.

Screenshot with commands in working order:
http://cl.ly/image/3V0n192R1p21

Tests Pass:
13 tests, 13 assertions, 0 failures
I couldn't get it to build to test the text displaying in browser, so
that still needs to be tested.

src/levels/intro/3.js

@@ -63,6 +63,7 @@ exports.level = {
             "To complete this level, do the following steps:",
             "",
             "* Make a new branch called `bugFix`",
+            "* Checkout the `bugFix` branch with `git checkout bugFix`",
             "* Commit once",
             "* Go back to `master` with `git checkout`",
             "* Commit another time",