Fix spelling (#2202)

context.go

@@ -1003,20 +1003,20 @@ func (c *Context) NegotiateFormat(offered ...string) string {
 		return offered[0]
 	}
 	for _, accepted := range c.Accepted {
-		for _, offert := range offered {
+		for _, offer := range offered {
 			// According to RFC 2616 and RFC 2396, non-ASCII characters are not allowed in headers,
 			// therefore we can just iterate over the string without casting it into []rune
 			i := 0
 			for ; i < len(accepted); i++ {
-				if accepted[i] == '*' || offert[i] == '*' {
-					return offert
+				if accepted[i] == '*' || offer[i] == '*' {
+					return offer
 				}
-				if accepted[i] != offert[i] {
+				if accepted[i] != offer[i] {
 					break
 				}
 			}
 			if i == len(accepted) {
-				return offert
+				return offer
 			}
 		}
 	}