Wrap nrfutil_path in quotes to avoid crash when the path includes spaces

[EEScott]

I was getting an error when trying to build on my machine where the user name has a space between and . The error I was getting is:

'C:\Users\Scott' is not recognized as an internal or external command, operable program or batch file.
*** [.pio\build\adafruit_feather_nrf52832\firmware.zip] Error 1

I only tested this for paths with a space and paths without a space.

[EEScott]

Actually, if I'm being thorough, I didn't check that it works for the other os_platforms (only tested win32):

if os_platform == "win32":
    nrfutil_path = join(FRAMEWORK_DIR, "tools", "adafruit-nrfutil", os_platform, "adafruit-nrfutil.exe")
elif os_platform == "darwin":
    nrfutil_path = join(FRAMEWORK_DIR, "tools", "adafruit-nrfutil", "macos", "adafruit-nrfutil")
else:
    nrfutil_path = "adafruit-nrfutil"

[EEScott]

I updated the PR to move the quotes into the path assignment because I got the same error when trying to upload to the board. I'm guessing this would also be a problem for the os_platform == "darwin" case, but I don't know how to test that so I didn't make a change there.