Fix critical mistake in parseTeXlog.py

[Jollywatt]

For parsing over/underfull messages, there is a line (504) that tests line == " []" — which is clearly meant to read line[-3:] == " []", since line is a string containing the entire line. (There are four other occurrences of line[-X:] == "…" in this file.)

Please accept this PR! It was impossible for me to continue working with LaTeXTools when log parsing was broken, but luckily the fix was trivial! :)