Fix typo in .gitignore

Fix typo in .gitignore

s/class_dump/class-dump
fix https://codereview.chromium.org/1161813003

Committed: https://crrev.com/cd45e416c1c4c2f8d07b509ef9d313aed2c49bfa
Cr-Commit-Position: refs/heads/master@{#332638}

[Olivier, 2015-06-03 17:09:20]

olivierrobin@chromium.org changed reviewers:
+ justincohen@chromium.org, sdefresne@chromium.org

[justincohen, 2015-06-03 17:10:26]

lgtm

[Olivier, 2015-06-03 17:13:46]

The CQ bit was checked by olivierrobin@chromium.org

[commit-bot: I haz the power, 2015-06-03 17:16:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1163073003/1

[commit-bot: I haz the power, 2015-06-03 17:16:46]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-06-03 17:16:47]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer,
_not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[sdefresne, 2015-06-03 17:45:21]

The CQ bit was checked by sdefresne@chromium.org

[sdefresne, 2015-06-03 17:45:22]

lgtm

[commit-bot: I haz the power, 2015-06-03 17:47:10]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1163073003/1

[commit-bot: I haz the power, 2015-06-03 17:58:37]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-03 17:59:20]

Patchset 1 (id:??) landed as
https://crrev.com/cd45e416c1c4c2f8d07b509ef9d313aed2c49bfa
Cr-Commit-Position: refs/heads/master@{#332638}