html.py doesn't specify pickle protocol version

*Originally reported by* **Anonymous**

----------------------------------------

html.py contains 
```
#!python

pickle.dump(status, fout)
```
which outputs version 3 data under python3, which then cannot be read under python2.x

Should be:
```
#!python

pickle.dump(status, fout, 2)
```

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- Bitbucket: https://bitbucket.org/ned/coveragepy/issue/287
