WIP: Relates to #281. Partly fixes yarn electron error. Error with sed running...

WIP: Relates to #281. Partly fixes yarn electron error. Error with sed running fixElectronBug script remains

Steps followed:

* Clone repo:
```
git clone https://github.com/paritytech/fether;
cd ./fether;
```

* Update Yarn and Copyfiles (for running script):
```
npm install --global yarn;
brew upgrade yarn;
npm install copyfiles -g;
```

* Upgrade to Babel 7
```
npx babel-upgrade --write
cd packages/fether-ui && npx babel-upgrade --write;
cd ../packages/fether-electron && npx babel-upgrade --write;
cd ../packages/fether-electron && npx babel-upgrade --write;
```

* Install dependencies:
```
yarn install;
```

* Run
```
yarn electron;
```

* Error due to `sed`

```
lerna ERR! build Errored while running script in 'fether'
lerna ERR! execute callback with error
lerna ERR! Error: Command failed: yarn run build
lerna ERR! sed: -e expression #1, char 7: missing command
lerna ERR! error Command failed with exit code 1.
lerna ERR! $ copyfiles -u 2 "../fether-react/build/**/*" static/ && "./scripts/fixElectronBug.sh"
lerna ERR! info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.
lerna ERR!
lerna ERR!     at Promise.all.then.arr (/Users/scon/code/src/paritytech/fether/node_modules/lerna/node_modules/execa/index.js:236:11)
{ Error: Command failed: yarn run build
sed: -e expression #1, char 7: missing command
error Command failed with exit code 1.
$ copyfiles -u 2 "../fether-react/build/**/*" static/ && "./scripts/fixElectronBug.sh"
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.

    at Promise.all.then.arr (/Users/scon/code/src/paritytech/fether/node_modules/lerna/node_modules/execa/index.js:236:11)
    at process._tickCallback (internal/process/next_tick.js:68:7)
  code: 1,
  killed: false,
  stdout:
   '$ copyfiles -u 2 "../fether-react/build/**/*" static/ && "./scripts/fixElectronBug.sh"\ninfo Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.\n',
  stderr:
   'sed: -e expression #1, char 7: missing command\nerror Command failed with exit code 1.\n',
  failed: true,
  signal: null,
  cmd: 'yarn run build',
  timedOut: false,
  exitCode: 1 }
error Command failed with exit code 1.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.
```