runes: fix ReadRune() to actually move the cursor

Signed-off-by: Alejandro Mery <[email protected]>

runes/reader.go

@@ -168,7 +168,8 @@ func (b *Reader) ReadRune() (rune, int, error) {
 
 	// decode rune
 	r, l := utf8.DecodeRune(b.buf[b.cursor:])
-
+	// step over
+	b.cursor += l
 	// and remember for UnreadRune()
 	b.lastRuneSize = l