Fix bug when lexing single-quoted strings

Single-quoted strings were accidentally expecting a double quote for
termination, instead of a single quote.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

src/syn/lexer.rs

@@ -59,7 +59,7 @@ impl<'t> Lexer<'t> {
             |(?P<hex_num>0[xX][0-9a-fA-F]+)
             |(?P<dec_num>[0-9]+)
             |(?P<dq_str>"([^\\"]|\\[ntr0"'])*")
-            |(?P<sq_str>'([^\\"]|\\[ntr0"'])*')
+            |(?P<sq_str>'([^\\']|\\[ntr0"'])*')
 
             |(?P<arrow>->)
             |(?P<eqeq>==)