uf2conv.py : Segment address of hex format must be added to address of each records #54

Sorry, I should have provided more thorough description in the previous issue #53 .

In this line above, it should be numerical addition.

so it must be like ...

addr = upper + ((rec[1] << 8) | rec[2] )

segment address must be multiplied by 16 and added to each subsequent data record address.

cf. https://en.wikipedia.org/wiki/Intel_HEX