Update variant for the ttgo-t-beam board

Resolves platformio#502

Author: cyberman54

boards/ttgo-t-beam.json

@@ -9,7 +9,7 @@
     "f_flash": "40000000L",
     "flash_mode": "dio",
     "mcu": "esp32",
-    "variant": "t-beam"
+    "variant": "tbeam"
   },
   "connectivity": [
     "wifi",