The Babel config had previously supported all browsers with greater than
0.25% global usage (according to `browserlist`). This resulted in
`babel-preset-env` including plugins sufficient to support the following
minimum browser versions:
```
{
"chrome": "49",
"android": "4.4",
"edge": "16",
"firefox": "52",
"ios": "9.3",
"safari": "11"
}
```
Instead, the babel config now explicitly supports chrome >= 58 and
firefox >= 53. Chrome and Firefox are the only browsers we currently
publish to, and these were the minimum versions with no additional Babel
transformations.
The minimum browser versions we support should be re-evaluated later,
when we have added tests and documentation.
The plugin 'transform-async-to-generator' has also been removed. It was
used to translate async/await, but our browser targets all support
async/await.
Removing some of these transformations exposed bugs in `uglify-es` that
only presented themselves in the production build. `gulp-uglify-es` has
been updated to a version that uses `terser` instead of `uglify-es`,
which has resolved these issues.
Relates to #6805
The `stage-0` Babel preset has been replaced with the specific Babel
plugins that we depend upon. We don't use most of `stage-0`, so this
allowed us to remove many unnecessary transformations. We had to remove
this preset soon anyway, because all of the stage presets are
deprecated in Babel 7.
The `stage-0` preset consisted of these plugins:
```
"transform-do-expressions"
"transform-function-bind"
"transform-class-constructor-call"
"transform-export-extensions"
"transform-class-properties"
"transform-decorators"
"syntax-dynamic-import"
"syntax-trailing-function-commas"
"transform-async-generator-functions"
"transform-async-to-generator"
"transform-exponentiation-operator"
"transform-object-rest-spread"
```
Of that list, only 'transform-class-properties', 'transform-object-
rest-spread', and 'transform-async-to-generator' were being used.
* Minimum supported browsers and version standard: add browsers and targets to .babelrc and package.json
* Regenerate package.json, fix issue with comma in merge
* Resolve merge conflicts
* Regenerate package-lock.json
* Revert to previous package-lock.json
