fix identifier -> keyword conversion

src/scanner.zig

@@ -249,6 +249,9 @@ pub const Scanner = struct {
             _ = self.advance();
         }
 
+        // ugly hack.
+        self.rollback();
+
         // after reading the identifier, we check
         // if it is any of our keywords, if it is, then we add
         // the specificed keyword type. if not, just .IDENTIFIER
@@ -261,9 +264,6 @@ pub const Scanner = struct {
             toktype = TokenType.Identifier;
         }
 
-        // ugly hack.
-        self.rollback();
-
         return self.makeToken(toktype);
     }