Update pattern-template.md

fixed typo: sentance -> sentence

Author: NewMexicoKid

meta/pattern-template.md

@@ -2,7 +2,7 @@
 Short Title Here
 
 ## Patlet
-Concise 1-2 sentance description of the problem and solution. Readers may quickly review dozens of these patlets to discover and browse the larger library of patterns. From http://wiki.c2.com/?PatLet
+Concise 1-2 sentence description of the problem and solution. Readers may quickly review dozens of these patlets to discover and browse the larger library of patterns. From http://wiki.c2.com/?PatLet
 
 ## Problem
 What is the problem - crisp definition of the problem. Short description, usually not more than a couple sentances, that describes what the issues and challenges are. Be careful not to morph into information found in other sections below.