Fixed bugs in vim keybindings.

There was a bug in findWord where lines containing no characters were
not being treated as words.

Example text:
```
word1

word2
```
In vim if the cursor is at line 0 column 0 and w is pressed, the expected
behavior is that the cursor will move to line 1 column 0.  In codemirror
the cursor was moving to line 2 column 0.

There remains a bug that if the cursor is on the 'o' in 'word1' and 'dw'
is pressed, 'ord1' is deleted, but the cursor remains where the 'o' used
to be.  (It should be on the 'w')