Do not enable flyspell-mode by default

Flyspell is probably too intrusive to be enabled by default.
Functionally it also depends on system's spell-checker configuration
which is outside of the scope of Git commit mode.

Signed-off-by: Teemu Likonen <tlikonen@iki.fi>
Merge pull request #95 from tlikonen/flyspell-off

Do not enable flyspell-mode by default