[pathkit] Add .ready() to initialize

See https://github.com/kripken/emscripten/issues/5820 and
https://skia-review.googlesource.com/c/skia/+/181177 for more context.

(Problem was discovered in CanvasKit, and this ports the same fix to
PathKit).

Bug: skia:
Change-Id: Ic8b2fb399210631a571595a5b3d11d1736c00def
Reviewed-on: https://skia-review.googlesource.com/c/181178
Reviewed-by: Joe Gregorio <jcgregorio@google.com>
diff --git a/modules/pathkit/tests/path2d.spec.js b/modules/pathkit/tests/path2d.spec.js
index a1bc763..6d505b7 100644
--- a/modules/pathkit/tests/path2d.spec.js
+++ b/modules/pathkit/tests/path2d.spec.js
@@ -9,7 +9,7 @@
         } else {
             PathKitInit({
                 locateFile: (file) => '/pathkit/'+file,
-            }).then((_PathKit) => {
+            }).ready().then((_PathKit) => {
                 PathKit = _PathKit;
                 resolve();
             });