Fix locEnd() for postcss parser (#2295)

* Fix locEnd() for postcss parser

`node.source` doesn't have an `end`, but `node.nodes[-1].source` does.

Fixes https://github.com/prettier/prettier/issues/2267

* Add regression test for https://github.com/prettier/prettier/issues/2267

See https://github.com/prettier/prettier/pull/2295#issuecomment-311484343

* Make locEnd() postcss fix more focused

This passes the tests again.

* Use getLast() instead of .slice()

See https://github.com/prettier/prettier/pull/2295#discussion_r124398553

* Move CSS range test into tests/range_css

This is so that the AST_COMPARE=1 tests don't try to parse CSS with Flow.

src/util.js

@@ -236,6 +236,11 @@ function locStart(node) {
 }
 
 function locEnd(node) {
+  const endNode = node.nodes && getLast(node.nodes);
+  if (endNode && node.source && !node.source.end) {
+    node = endNode;
+  }
+
   let loc;
   if (node.range) {
     loc = node.range[1];

tests/range_css/__snapshots__/jsfmt.spec.js.snap

@@ -0,0 +1,8 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`issue2267.css 1`] = `
+.x{} 
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+.x{} 
+
+`;

tests/range_css/issue2267.css

@@ -0,0 +1 @@
+.x{}<<<PRETTIER_RANGE_END>>> 

tests/range_css/jsfmt.spec.js

@@ -0,0 +1 @@
+run_spec(__dirname, { parser: "postcss" });