Fix es5 builds

gulp/yarn.lock

@@ -1240,6 +1240,11 @@ acorn@^6.0.1, acorn@^6.0.2, acorn@^6.0.7, acorn@^6.4.1:
   resolved "https://registry.npmjs.org/acorn/-/acorn-6.4.1.tgz"
   integrity sha512-ZVA9k326Nwrj3Cj9jlh3wGFutC2ZornPNARZwsNYqQYgN0EsV2d53w5RN/co65Ohn4sUAUtb1rSUAOD6XN9idA==
 
+acorn@^6.0.6:
+  version "6.4.2"
+  resolved "https://registry.yarnpkg.com/acorn/-/acorn-6.4.2.tgz#35866fd710528e92de10cf06016498e47e39e1e6"
+  integrity sha512-XtGIhXwF8YM8bJhGxG5kXgjkEuNGLTkoYqVE+KMR+aspr4KGYmKYg7yUe3KghyQ9yheNwLnjmzh/7+gfDBmHCQ==
+
 after@0.8.2:
   version "0.8.2"
   resolved "https://registry.npmjs.org/after/-/after-0.8.2.tgz"
@@ -1465,6 +1470,16 @@ archy@^1.0.0:
   resolved "https://registry.npmjs.org/archy/-/archy-1.0.0.tgz"
   integrity sha1-+cjBN1fMHde8N5rHeyxipcKGjEA=
 
+are-you-es5@^2.1.2:
+  version "2.1.2"
+  resolved "https://registry.yarnpkg.com/are-you-es5/-/are-you-es5-2.1.2.tgz#d75511a174a3f842d70cc784aec0bcaff5a57547"
+  integrity sha512-gkT2bLCfzyJJr3lYoxZKScdD/Yp5zzghi+3KawONTvH/7rrgU3RMXYvGQnOTlqEFVgZFpEGj/6bZ6sF/9YtddA==
+  dependencies:
+    acorn "^6.0.6"
+    array-flatten "^2.1.0"
+    commander "^2.19.0"
+    find-up "^4.1.0"
+
 argparse@^1.0.7:
   version "1.0.10"
   resolved "https://registry.npmjs.org/argparse/-/argparse-1.0.10.tgz"
@@ -1534,6 +1549,11 @@ array-find-index@^1.0.1:
   resolved "https://registry.npmjs.org/array-find-index/-/array-find-index-1.0.2.tgz"
   integrity sha1-3wEKoSh+Fku9pvlyOwqWoexBh6E=
 
+array-flatten@^2.1.0:
+  version "2.1.2"
+  resolved "https://registry.yarnpkg.com/array-flatten/-/array-flatten-2.1.2.tgz#24ef80a28c1a893617e2149b0c6d0d788293b099"
+  integrity sha512-hNfzcOV8W4NdualtqBFPyVO+54DSJuZGY9qT4pRroB6S9e3iiido2ISIC5h9R2sPJ8H3FHCIiEnsv1lPXO3KtQ==
+
 array-initial@^1.0.0:
   version "1.1.0"
   resolved "https://registry.npmjs.org/array-initial/-/array-initial-1.1.0.tgz"