Update Polymer components.

third_party/polymer/components/iron-flex-layout/bower.json

Index: third_party/polymer/components/iron-flex-layout/bower.json
diff --git a/third_party/polymer/components/iron-flex-layout/bower.json b/third_party/polymer/components/iron-flex-layout/bower.json
index 30c6afe4c7b72616fa64146abc84ce95c84af3a6..7b6b1a2cd7c4ef02813e66395cc9be684b6055c4 100644
--- a/third_party/polymer/components/iron-flex-layout/bower.json
+++ b/third_party/polymer/components/iron-flex-layout/bower.json
@@ -1,6 +1,6 @@
 {
   "name": "iron-flex-layout",
-  "version": "1.3.2",
+  "version": "1.3.7",
   "description": "Provide flexbox-based layouts",
   "keywords": [
     "web-components",
@@ -27,5 +27,8 @@
     "webcomponentsjs": "webcomponents/webcomponentsjs#^0.7.0",
     "web-component-tester": "^4.0.0"
   },
+  "pages": {
+    "Flexbox layout guide": "GUIDE.md"
+  },
   "ignore": []
 }