Use correct forms of "criterion" (singular) and "criteria" (plural)

[DePasqualeOrg]

I submitted a small pull request to correct the usage of the words criterion and criteria in the language-tools package, but apparently these corrections need to be made in this package first, and I noticed that the usage of these words is quite a bit more extensive here. For reference:

• criterion is the singular form.
• criteria is the plural form.
• criterias is not an accepted form in English.