Correctly provide default value for DRIP_POOL
Correctly provide default value for DRIP_POOL

This syntax matches all other default values.  Previously this failed
with:

/home/gaul/bin/drip: line 223: ((: 0 <  : syntax error: operand expected (error token is "<  ")

ninjudd/drip,mjwall/drip,ninjudd/drip,mjwall/drip,mjwall/drip,ninjudd/drip