feat: update lib compiler option to es2018 (#956)

BREAKING CHANGE:

The following `peerDependencies` are now required
- `tslib: ^1.9.0`
- `typescript: ^2.7.0`

The default for `lib.languageLevel`  is now `es2018`. In case this needs to be changed. This can to be done by overriding the tsconfig. More on how to override the tsconfig can be found here: https://github.com/dherges/ng-packagr/blob/master/docs/override-tsconfig.md

Author: alan-agius4

package.json

@@ -58,8 +58,8 @@
     "@angular/compiler": "^6.0.0",
     "@angular/compiler-cli": "^6.0.0",
     "tsickle": ">=0.27.3",
-    "tslib": "^1.7.1",
-    "typescript": ">=2.4.2"
+    "tslib": "^1.9.0",
+    "typescript": "^2.7.0"
   },
   "devDependencies": {
     "@angular-devkit/core": "^0.6.0",

src/lib/ts/conf/tsconfig.ngc.json

@@ -24,7 +24,7 @@
     "emitDecoratorMetadata": true,
     "experimentalDecorators": true,
     "importHelpers": true,
-    "lib": ["dom", "es2015"]
+    "lib": ["dom", "es2018"]
   },
   "exclude": ["node_modules", "dist", "**/*.ngfactory.ts", "**/*.shim.ts", "**/*.spec.ts"],
   "files": ["AUTOGENERATED"]