fix: show TX15 and T15Pro for RCs (#137)

Author: pfeerick

targets.json

@@ -287,7 +287,7 @@
     },
     "t15pro": {
       "description": "Jumper T15 Pro",
-      "version_supported": ">= v2.12.0",
+      "version_supported": ">= v2.12.0-RC1",
       "tags": ["colorlcd", "bluetooth"]
     },
     "t16": {
@@ -361,7 +361,7 @@
     },
     "tx15": {
       "description": "RadioMaster TX15",
-      "version_supported": ">= v2.12.0",
+      "version_supported": ">= v2.12-RC1",
       "tags": ["colorlcd"]
     },
     "tx16s": {