Fix MKS Robin python script (for Travis CI) (#15523)

.travis.yml

   - TEST_PLATFORM="jgaurora_a5s_a1"
   - TEST_PLATFORM="STM32F103VE_longer"
   - TEST_PLATFORM="STM32F407VE_black"
+  - TEST_PLATFORM="mks_robin"
 
   # Put lengthy tests last
   - TEST_PLATFORM="LPC1768"
   #- TEST_PLATFORM="at90usb1286_cdc"
   #- TEST_PLATFORM="at90usb1286_dfu"
   #- TEST_PLATFORM="STM32F103CB_malyan"
-  #- TEST_PLATFORM="mks_robin"
   #- TEST_PLATFORM="mks_robin_lite"
   #- TEST_PLATFORM="mks_robin_mini"
   #- TEST_PLATFORM="mks_robin_nano"

buildroot/share/PlatformIO/scripts/mks_robin.py

 # Encrypt ${PROGNAME}.bin and save it as 'Robin.bin'
 def encrypt(source, target, env):
     import os
+    import sys
 
     key = [0xA3, 0xBD, 0xAD, 0x0D, 0x41, 0x11, 0xBB, 0x8D, 0xDC, 0x80, 0x2D, 0xD0, 0xD2, 0xC4, 0x9B, 0x1E, 0x26, 0xEB, 0xE3, 0x33, 0x4A, 0x15, 0xE4, 0x0A, 0xB3, 0xB1, 0x3C, 0x93, 0xBB, 0xAF, 0xF7, 0x3E]
 
             byte = firmware.read(1)
             if position >= 320 and position < 31040:
                 byte = chr(ord(byte) ^ key[position & 31])
+                if sys.version_info[0] > 2:
+                    byte = bytes(byte, 'latin1')
             robin.write(byte)
             position += 1
     finally:

buildroot/share/PlatformIO/scripts/mks_robin_lite.py

 # Encrypt ${PROGNAME}.bin and save it as 'mksLite.bin'
 def encrypt(source, target, env):
     import os
+    import sys
 
     key = [0xA3, 0xBD, 0xAD, 0x0D, 0x41, 0x11, 0xBB, 0x8D, 0xDC, 0x80, 0x2D, 0xD0, 0xD2, 0xC4, 0x9B, 0x1E, 0x26, 0xEB, 0xE3, 0x33, 0x4A, 0x15, 0xE4, 0x0A, 0xB3, 0xB1, 0x3C, 0x93, 0xBB, 0xAF, 0xF7, 0x3E]
 
             byte = firmware.read(1)
             if position >= 320 and position < 31040:
                 byte = chr(ord(byte) ^ key[position & 31])
+                if sys.version_info[0] > 2:
+                    byte = bytes(byte, 'latin1')
             robin.write(byte)
             position += 1
     finally:

buildroot/share/PlatformIO/scripts/mks_robin_mini.py

 # Encrypt ${PROGNAME}.bin and save it as 'Robin_mini.bin'
 def encrypt(source, target, env):
     import os
+    import sys
 
     key = [0xA3, 0xBD, 0xAD, 0x0D, 0x41, 0x11, 0xBB, 0x8D, 0xDC, 0x80, 0x2D, 0xD0, 0xD2, 0xC4, 0x9B, 0x1E, 0x26, 0xEB, 0xE3, 0x33, 0x4A, 0x15, 0xE4, 0x0A, 0xB3, 0xB1, 0x3C, 0x93, 0xBB, 0xAF, 0xF7, 0x3E]
 
             byte = firmware.read(1)
             if position >= 320 and position < 31040:
                 byte = chr(ord(byte) ^ key[position & 31])
+                if sys.version_info[0] > 2:
+                    byte = bytes(byte, 'latin1')
             robin.write(byte)
             position += 1
     finally:

buildroot/share/PlatformIO/scripts/mks_robin_nano.py

 # Encrypt ${PROGNAME}.bin and save it as 'Robin_nano.bin'
 def encrypt(source, target, env):
     import os
+    import sys
 
     key = [0xA3, 0xBD, 0xAD, 0x0D, 0x41, 0x11, 0xBB, 0x8D, 0xDC, 0x80, 0x2D, 0xD0, 0xD2, 0xC4, 0x9B, 0x1E, 0x26, 0xEB, 0xE3, 0x33, 0x4A, 0x15, 0xE4, 0x0A, 0xB3, 0xB1, 0x3C, 0x93, 0xBB, 0xAF, 0xF7, 0x3E]
 
             byte = firmware.read(1)
             if position >= 320 and position < 31040:
                 byte = chr(ord(byte) ^ key[position & 31])
+                if sys.version_info[0] > 2:
+                    byte = bytes(byte, 'latin1')
             robin.write(byte)
             position += 1
     finally: