Correct Documentation For DEC Function

The documentation for DEC in func_math.c was incorrect.  Looks like a copy and
paste error.

(Closes issue ASTERISK-20095)
Reported by: Billy Chia
Tested by: Michael L. Young
Patches:
    func_math.patch uploaded by Billy Chia (license 6381)
........

Merged revisions 369970 from http://svn.asterisk.org/svn/asterisk/branches/1.8


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@369972 65c4cc65-6c06-0410-ace0-fbb531ad65f3

funcs/func_math.c

@@ -103,8 +103,8 @@ ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
 		</syntax>
 		<description>
 			<para>Decrements the value of a variable, while returning the updated value to the dialplan</para>
-			<para>Example: DEC(MyVAR) - Increments MyVar</para>
-			<para>Note: DEC(${MyVAR}) - Is wrong, as INC expects the variable name, not its value</para>
+			<para>Example: DEC(MyVAR) - Decrements MyVar</para>
+			<para>Note: DEC(${MyVAR}) - Is wrong, as DEC expects the variable name, not its value</para>
 		</description>
 	</function>
  ***/