update minimum supported version to 2018.4

Author: vkovec

.yamato/upm-ci.yml

@@ -2,7 +2,6 @@ test_trigger_editors:
   - version: 2018.4
   - version: 2019.4
 publish_trigger_editors:
-  - version: 2018.3
   - version: 2018.4
   - version: 2019.1
   - version: 2019.2

CHANGELOG.md

@@ -10,6 +10,7 @@
 - Renamed Export as FBX Linked Prefab to Export as FBX Prefab Variant.
 - Mesh instances are now exported as instances of a single mesh instead of exporting multiple, identical meshes.
 - Updated to latest com.autodesk.fbx (3.1.0-preview.2).
+- Updated minimum supported Unity version to 2018.4.
 
 ### Fixed
 - No longer initiate export if no objects are selected in Autodesk® 3ds Max®.

com.unity.formats.fbx/package.json

@@ -7,8 +7,8 @@
     "com.unity.timeline": "1.0.0",
     "com.autodesk.fbx": "3.1.0-preview.2"
   },
-  "unity": "2018.3",
-  "unityRelease": "4f1",
+  "unity": "2018.4",
+  "unityRelease": "0f1",
   "description": "The Unity FBX Exporter package makes it easy to send geometry and animation from Unity 2018.3 or later to any application that supports FBX and back again with minimal effort.\n\nIn particular, this round-trip workflow enables you to export Unity scenes to FBX, import into Maya, Maya LT, or 3ds Max using an artist-friendly interface, export Unity-ready FBX geometry and animation, and safely merge your changes back into those Assets to continue your work.\n\nFor more information, see the FBX Exporter package documentation.",
   "keywords": [
     "fbx",