Changed TeX to not ignore tikz files by default. (#3320)

TeX.gitignore

@@ -135,8 +135,8 @@ acs-*.bib
 
 # knitr
 *-concordance.tex
-# TODO Comment the next line if you want to keep your tikz graphics files
-*.tikz
+# TODO Uncomment the next line if you use knitr and want to ignore its generated tikz files
+# *.tikz
 *-tikzDictionary
 
 # listings