Update to defmt 0.2.0

[jonas-schievink]

bors r+

[bors[bot]]

Build failed:

• ci

[jonas-schievink]

bors retry

[bors[bot]]

Build failed:

• ci

[jonas-schievink]

bors retry

[bors[bot]]

Build failed:

• ci

[jonas-schievink]

2021-03-03T14:34:22.3474969Z RTT error: Error communicating with probe: A core architecture specific error occured
2021-03-03T14:34:22.4791910Z Error: A core architecture specific error occured
2021-03-03T14:34:22.4793832Z 
2021-03-03T14:34:22.4795396Z Caused by:
2021-03-03T14:34:22.4970452Z     0: Failed to read register DRW at address 0x0000000c
2021-03-03T14:34:22.4974461Z     1: Received invalid data for 5
2021-03-03T14:34:22.4977493Z     2: Unexpected answer to command

???

[jonas-schievink]

bors r+ (replugged the target)

[bors[bot]]

Build failed:

• ci

[jonas-schievink]

bors retry

[jonas-schievink]

Error: An error with the usage of the probe occured

Caused by:
    Unexpected answer to command

????

[bors[bot]]

Build failed:

• ci

[jonas-schievink]

bors retry

[bors[bot]]

Build succeeded:

• ci