rename yunmini.bootloader.file on boards.txt

Author: gigoh

Diff for: boards.txt

@@ -946,7 +946,7 @@ yunmini.bootloader.tool=avrdude
 yunmini.bootloader.low_fuses=0xff
 yunmini.bootloader.high_fuses=0xd8
 yunmini.bootloader.extended_fuses=0xfb
-yunmini.bootloader.file=caterina/Caterina-Yunmini.hex
+yunmini.bootloader.file=caterina/Caterina-YunMini.hex
 yunmini.bootloader.unlock_bits=0x3F
 yunmini.bootloader.lock_bits=0x2F