fix(spellchecker): Preliminary Linux support
fix(spellchecker): Preliminary Linux support

The Linux component of Atom's spellchecker depends on Hunspell for
corrections. It requires a dictionary to be set, unlike Mac OS X
and Windows that have spellcheckers built in to the OS, and they
have the dictionaries built-in as well. This commit uses Atom's
spellchecker default dictionary method (which I wish was a public
API) to reset the dictionary to its default setting. It also ignores
the dictionaries available command for the Linux platform, which
seems to always return an empty Array.

simonft/nylas-mail,nylas/nylas-mail,nylas/nylas-mail,nylas-mail-lives/nylas-mail,nylas/nylas-mail,nylas/nylas-mail,simonft/nylas-mail,nirmit/nylas-mail,nylas-mail-lives/nylas-mail,simonft/nylas-mail,simonft/nylas-mail,nylas-mail-lives/nylas-mail,nylas-mail-lives/nylas-mail,nirmit/nylas-mail,nirmit/nylas-mail,nirmit/nylas-mail,nylas-mail-lives/nylas-mail,simonft/nylas-mail,nirmit/nylas-mail,nylas/nylas-mail