correct spelling mistake

Author: EdwardBetts

README.md

@@ -108,7 +108,7 @@ Normally, no arguments are required for the constructor, but you can initialise
 var bl = require('bl')
 var myinstance = bl()
 
-// equivilant to:
+// equivalent to:
 
 var BufferList = require('bl')
 var myinstance = new BufferList()