Fix scala-js/scala-js#2376: PhantomJSEnv does not escape JS code

Author: gzm0

js-envs-test-kit/src/main/scala/org/scalajs/jsenv/test/BasicJSEnvTests.scala

@@ -34,4 +34,13 @@ trait BasicJSEnvTests extends JSEnvTest {
 
   }
 
+  @Test
+  def allowScriptTags: Unit = {
+
+    """
+    console.log("<script></script>");
+    """ hasOutput "<script></script>\n";
+
+  }
+
 }