Drop support for Ember 3.19 and below

Author: Turbo87

README.md

@@ -386,7 +386,8 @@ module.exports = {
 
 ## Dependencies
 
-* For Ember versions >= 2.8, use the latest published version (Note that ember-cli >= 2.13 is required, though your ember version may be >= 2.8)
+* For Ember versions >= 3.20, use the latest published version
+* For Ember versions >= 2.8 and < 3.20, use the latest 3.x version (Note that ember-cli >= 2.13 is required, though your ember version may be >= 2.8)
 * For Ember versions >= 2.4 and < 2.8, use the latest 2.x version
 * For Ember versions >= 1.10 and < 2.4, use ember-modal-dialog 1.0.0 _(Due to a bug in these versions of Ember, you may have trouble with Ember 1.13.7, 1.13.8 and 1.13.9 -- See #71)_
 

package.json

@@ -76,7 +76,7 @@
     "configPath": "tests/dummy/config",
     "demoURL": "http://yapplabs.github.io/ember-modal-dialog/",
     "versionCompatibility": {
-      "ember": "~2.8.0 || ~2.12.0 || ~2.16.0 || ~2.18.0 || ~3.0.0 || ~3.4.0 ||  ~3.8.0 ||  ~3.12.0 ||  ~3.16.0 || > 3.17.0"
+      "ember": "~3.20.0 ||  ~3.24.0 || >= 3.25.0"
     }
   },
   "release-it": {