update package index for release 2.5.1

Author: Travis CI

stable/package_esp8266com_index.json

@@ -1,9 +1,3 @@
-Dropping version 1.6.5-947-g39819f0
-Dropping version 2.5.0-beta1
-Dropping version 2.5.0-beta2
-Dropping version 2.5.0-beta3
-Dropping version 2.4.0-rc1
-Dropping version 2.4.0-rc2
 {
   "packages": [
     {
@@ -746,7 +740,7 @@ Dropping version 2.4.0-rc2
             "online": "https://arduino-esp8266.readthedocs.io/en/2.5.1/"
           }, 
           "url": "https://github.com/esp8266/Arduino/releases/download/2.5.1/esp8266-2.5.1.zip", 
-          "checksum": "SHA-256:77874cf43f9bb22024ed9f23296517854c8d4cd8352a5ded27b60c90d2af6873", 
+          "checksum": "SHA-256:a433b764ca75d90c3df632949ff91777afe06e4e07a691cd68e7cf8c51eafc8c", 
           "version": "2.5.1", 
           "architecture": "esp8266", 
           "archiveFileName": "esp8266-2.5.1.zip",