Fix no-invalid-this issues (#9207)

See [`no-invalid-this`](https://eslint.org/docs/rules/no-invalid-this) for more information.

This change enables `no-invalid-this` and fixes the issues raised by the rule.

.eslintrc.js

@@ -105,6 +105,10 @@ module.exports = {
       'logical': 'parens-new-line',
       'prop': 'parens-new-line',
     }],
+
+    'no-invalid-this': 'off',
+    'babel/no-invalid-this': 'error',
+
     'babel/semi': ['error', 'never'],
     'mocha/no-setup-in-describe': 'off',
   },
@@ -124,6 +128,15 @@ module.exports = {
     rules: {
       'global-require': 'off',
     },
+  }, {
+    files: [
+      'test/**/*-test.js',
+      'test/**/*.spec.js',
+    ],
+    rules: {
+      // Mocha will re-assign `this` in a test context
+      'babel/no-invalid-this': 'off',
+    },
   }],
 
   settings: {

app/scripts/controllers/transactions/tx-state-manager.js

@@ -164,10 +164,10 @@ export default class TransactionStateManager extends EventEmitter {
       txMeta.txParams = this.normalizeAndValidateTxParams(txMeta.txParams)
     }
 
-    this.once(`${txMeta.id}:signed`, function () {
+    this.once(`${txMeta.id}:signed`, () => {
       this.removeAllListeners(`${txMeta.id}:rejected`)
     })
-    this.once(`${txMeta.id}:rejected`, function () {
+    this.once(`${txMeta.id}:rejected`, () => {
       this.removeAllListeners(`${txMeta.id}:signed`)
     })
     // initialize history

ui/app/components/app/gas-customization/gas-price-chart/gas-price-chart.utils.js

@@ -124,6 +124,7 @@ export function setTickPosition (axis, n, newPosition, secondNewPosition) {
     .style('visibility', 'visible')
 }
 
+/* eslint-disable babel/no-invalid-this */
 export function appendOrUpdateCircle ({ data, itemIndex, cx, cy, cssId, appendOnly }) {
   const circle = this.main
     .select('.c3-selected-circles' + this.getTargetSelectorSuffix(data.id))
@@ -144,6 +145,7 @@ export function appendOrUpdateCircle ({ data, itemIndex, cx, cy, cssId, appendOn
       .attr('cy', cy)
   }
 }
+/* eslint-enable babel/no-invalid-this */
 
 export function setSelectedCircle ({
   chart,