Fix a pluralization error

Author: jbranchaud

postgres/escaping-a-quote-in-a-string.md

@@ -1,6 +1,6 @@
 # Escaping A Quote In A String
 
-In PostgreSQL, strings (`varchar` and `text`) literals are declared with
+In PostgreSQL, string (`varchar` and `text`) literals are declared with
 single quotes (`'`). That means that any string containing a single quote as
 part of the content of the string will need some escaping. The way to escape
 a single quote is with another single quote.