fix: create regexp literal if possible (#308)

to get around not serializable regexp the raw literal value should be used instead of the value

FIX ISSUE #294
diff --git a/escodegen.js b/escodegen.js
index 6202819..42c05ae 100644
--- a/escodegen.js
+++ b/escodegen.js
@@ -2331,6 +2331,9 @@
                 return expr.value ? 'true' : 'false';
             }
 
+            if (expr.regex) {
+              return '/' + expr.regex.pattern + '/' + expr.regex.flags;
+            }
             return generateRegExp(expr.value);
         },