feat(core): upgrade dependencies for Angular v8+ (#1094)

BREAKING CHANGE: Angular v8+ is now required

Author: peterblazejewicz

README.md

@@ -48,7 +48,8 @@ Choose the version corresponding to your Angular version:
 
  Angular     | @ngx-translate/core | @ngx-translate/http-loader
  ----------- | ------------------- | --------------------------
- 7/8         | 11.x+               | 4.x+
+ 8           | 12.x+               | 4.x+
+ 7           | 11.x+               | 4.x+
  6           | 10.x                | 3.x
  5           | 8.x to 9.x          | 1.x to 2.x
  4.3         | 7.x or less         | 1.x to 2.x