Fix infinite loop when parsing strings

examples_out/out.js

@@ -1,6 +1,6 @@
 function main() {
-return;
+return "Hello World"
 }
 function fib() {
 }
-main()
+console.log(main())

src/lexer/mod.rs

@@ -288,6 +288,11 @@ impl Cursor<'_> {
         loop {
             match self.first() {
                 '"' | '\'' => break,
+                '\n' => panic!(
+                    "String does not end on same line. At {}:{}",
+                    self.pos().line,
+                    self.pos().offset
+                ),
                 _ => self.bump(),
             };
         }