fixes #2521: line numbers in errors affected by newlines in backticks

lib/coffee-script/lexer.js

@@ -217,6 +217,7 @@
         return 0;
       }
       this.token('JS', (script = match[0]).slice(1, -1));
+      this.line += count(script, '\n');
       return script.length;
     };
 

src/lexer.coffee

@@ -197,6 +197,7 @@ exports.Lexer = class Lexer
   jsToken: ->
     return 0 unless @chunk.charAt(0) is '`' and match = JSTOKEN.exec @chunk
     @token 'JS', (script = match[0])[1...-1]
+    @line += count script, '\n'
     script.length
 
   # Matches regular expression literals. Lexing regular expressions is difficult