Fix various errors

[andygup]

• Fixed small linter errors in styles.ts
• Removes trailing slash from preview copy in scaffold.ts
• Removes copy commands from cleanDirectories.ts

Tested locally - creating themes and new widgets seems to be working again.

Related: #105, #106

[odoe]

This looks like this is working for me locally. Can someone test on Windows to be sure?

[jcfranco]

Awesome, thanks!

[andygup]

@odoe I added d4233ee to replace fs-extra with cpy in createWidget.ts.

This fix attempts to resolve a known issue with fs-extra that throws Error: Widget creation failed: Source and destination must not be the same. I see that fs-extra is used in three other places, so this may not be a complete fix.

Here's the full error dump:

Error: Widget creation failed: Source and destination must not be the same.
    at _callee$ (/Users/xyz/.volta/tools/image/packages/@arcgis/cli/lib/node_modules/@arcgis/cli/dist/lib/createWidget.js:142:61)
    at tryCatch (/Users/xyz/.volta/tools/image/packages/@arcgis/cli/lib/node_modules/@arcgis/cli/node_modules/regenerator-runtime/runtime.js:63:40)
    at Generator.invoke [as _invoke] (/Users/xyz/.volta/tools/image/packages/@arcgis/cli/lib/node_modules/@arcgis/cli/node_modules/regenerator-runtime/runtime.js:294:22)
    at Generator.throw (/Users/xyz/.volta/tools/image/packages/@arcgis/cli/lib/node_modules/@arcgis/cli/node_modules/regenerator-runtime/runtime.js:119:21)
    at asyncGeneratorStep (/Users/xyz/.volta/tools/image/packages/@arcgis/cli/lib/node_modules/@arcgis/cli/dist/lib/createWidget.js:56:22)
    at _throw (/Users/xyz/.volta/tools/image/packages/@arcgis/cli/lib/node_modules/@arcgis/cli/dist/lib/createWidget.js:66:291)

References: jprichardson/node-fs-extra#657

On a side note, I also noticed that the npm installed build has an async generator in createWidget.js and my local build does not. We may want to set a TS target?