Update rollup to latest

This release of rollup contains a fix that means babel helpers in the
esm build get generated with a .mjs extension, rather than a .js
extension.

This fixes an error that occures when trying to use the esm build in
node. See rollup/plugins#1031

yarn.lock

@@ -7307,7 +7307,7 @@ fsevents@^1.2.7:
     nan "^2.12.1"
     node-pre-gyp "^0.12.0"
 
-fsevents@^2.3.2, fsevents@~2.3.1:
+fsevents@^2.3.2, fsevents@~2.3.1, fsevents@~2.3.2:
   version "2.3.2"
   resolved "https://registry.yarnpkg.com/fsevents/-/fsevents-2.3.2.tgz#8a526f78b8fdf4623b709e0b975c52c24c02fd1a"
   integrity sha512-xiqMQR4xAeHTuB9uWm+fFRcIOgKBMiOBP+eXiyT7jsgVCq1bkVygt00oASowB7EdtpOHaaPgKt812P9ab+DDKA==
@@ -12372,11 +12372,11 @@ rollup-plugin-node-externals@^2.2.0:
     find-up "^4.1.0"
 
 rollup@^2.48.0:
-  version "2.48.0"
-  resolved "https://registry.yarnpkg.com/rollup/-/rollup-2.48.0.tgz#fceb01ed771f991f29f7bd2ff7838146e55acb74"
-  integrity sha512-wl9ZSSSsi5579oscSDYSzGn092tCS076YB+TQrzsGuSfYyJeep8eEWj0eaRjuC5McuMNmcnR8icBqiE/FWNB1A==
+  version "2.60.1"
+  resolved "https://registry.yarnpkg.com/rollup/-/rollup-2.60.1.tgz#4b34cd247f09b421f10a3c9286eda2ecf9972079"
+  integrity sha512-akwfnpjY0rXEDSn1UTVfKXJhPsEBu+imi1gqBA1ZkHGydUnkV/fWCC90P7rDaLEW8KTwBcS1G3N4893Ndz+jwg==
   optionalDependencies:
-    fsevents "~2.3.1"
+    fsevents "~2.3.2"
 
 run-async@^2.4.0:
   version "2.4.0"