This pull-request upgrades `ethereumjs-wallet`, which has upgraded the underlying dependency on scrypt.js to 0.3.0, making scrypt an optional dependency and offering a pure JS version as a fallback.
The reasoning behind this is that scrypt is problematic to install in some systems, particularly those that don't have node-gyp setup and we have seen some weird issues when installing with elevated privileges (i.e. `sudo npm install -g scrypt`)
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