Correct variable definition statement.

proofit404 · proofit404 · commit 528527c83271 · 2018-04-02T14:35:45.000+03:00
diff --git a/blacken.el b/blacken.el
@@ -47,7 +47,7 @@
   "Name of the executable to run."
   :type 'string)
 
-(defvar blacken-line-length nil
+(defcustom blacken-line-length nil
   "Line length to enforce."
   :type 'number)
 
