make indexOf() checks consistent

The use of `ua.indexOf( "PlayBook" ) > -1` and ` !ua.indexOf( "Android 2" ) === -1` on the same line made me go: "Wait, aren't those both checking for the presence of a string in `ua`? Or are they subtly different and I'm just missing something? I'm totally confused."

Since they are, in fact, both checking that the return value is 0 or above, I changed the second one to the format of the first one. I mean, I guess it doesn't really matter, but it should probably be one or the other and not both...

Although I also don't see "Android 2" in the UA string in the comment above. So now I'm puzzled again. Bug?