Fix unterminated string in rfcbot grammar (#285)

Author: marvin-bitterlich

README.md

@@ -48,7 +48,7 @@ rfcbot accepts roughly the following grammar:
 merge ::= "merge" | "merged" | "merging" | "merges" ;
 close ::= "close" | "closed" | "closing" | "closes" ;
 postpone ::= "postpone" | "postponed" | "postponing" | "postpones" ;
-cancel ::= "cancel | "canceled" | "canceling" | "cancels" ;
+cancel ::= "cancel" | "canceled" | "canceling" | "cancels" ;
 review ::= "reviewed" | "review" | "reviewing" | "reviews" ;
 concern ::= "concern" | "concerned" | "concerning" | "concerns" ;
 resolve ::= "resolve" | "resolved" | "resolving" | "resolves" ;