build: bump yarn requirement to 1.17.3

Author: josephperrott

.circleci/config.yml

@@ -64,7 +64,7 @@ var_10: &yarn_download
     name: "Downloading and installing Yarn"
     command: |
       touch $BASH_ENV
-      curl -o- -L https://yarnpkg.com/install.sh | PROFILE=$BASH_ENV bash -s -- --version "1.16.0"
+      curl -o- -L https://yarnpkg.com/install.sh | PROFILE=$BASH_ENV bash -s -- --version "1.17.3"
 
 # Sets up the Bazel config which is specific for CircleCI builds.
 var_11: &setup_bazel_ci_config

package.json

@@ -10,7 +10,7 @@
   "license": "MIT",
   "engines": {
     "node": ">= 5.4.1",
-    "yarn": ">= 1.13.0"
+    "yarn": ">= 1.17.3"
   },
   "scripts": {
     "postinstall": "ngc -p angular-tsconfig.json",