de-lint MegolmExportEncryption + test

test/.eslintrc.js

@@ -2,4 +2,9 @@ module.exports = {
     env: {
         mocha: true,
     },
-}
+
+    // mocha defines a 'this'
+    rules: {
+        "babel/no-invalid-this": "off",
+    },
+};