Update sqlite3 amalgamation version

[ksylvest]

Running on XCode 6.2 the library currently has 30 warnings in keen_io_sqlite3.c.

[heitortsergent]

Hey @ksylvest, I'm looking into this. Just ran the static analyzer and it gave me 24 issues:

Would you mind double-checking that Xcode gave out 30 warnings? I don't wanna miss any of them. :)

[ksylvest]

I've since upgrade to XCode 6.3 and it shows 32 issues:

Thanks!

[heitortsergent]

@ksylvest I dug into this a little further and the keen_io_sqlite3 is just the amalgamation of the regular sqlite3 library, so the errors should be nothing more than false positives.

That said, the version we have in the library is outdated, so I'm gonna change the issue title to update the current version of the sqlite3 library