Fix dependencies so that yarn --ignore-engines is not necessary and node 11 works

[ragesoss]

We get a lot of problems lately related to yarn and node versions...

In particular, linux users (among others?) must run yarn --ignore-engines to get yarn to properly install the node modules, and node 11 is not compatible with the build process (at least, on travis-ci).

Fixing whatever version incompatibilties prevent us from using the latest node and the vanilla yarn command would save a lot of pain for new contributors.

[khyatisoneji]

@ragesoss I found a fix for this issue here: enzymejs/enzyme#1637 (comment)

With this fix, only thing that I need to change in yarn.lock file is the version of upath.

Basically the diff is this:

 upath@^1.0.0:
-  version "1.0.4"
-  resolved "https://registry.yarnpkg.com/upath/-/upath-1.0.4.tgz#ee2321ba0a786c50973db043a50b7bcba822361d"
+  version "1.1.0"
+  resolved "https://registry.yarnpkg.com/upath/-/upath-1.1.0.tgz#35256597e46a581db4793d0ce47fa9aebfc9fabd"
   integrity sha512-d4SJySNBXDaQp+DPrziv3xGS6w3d2Xt69FijJr86zMPBy23JEloMCEOUBBzuN7xCtjLCnmB9tI/z7SBCahHBOw==

Should I send in a PR for this?