Update := and with=FALSE usage

[boxuancui]

Warning message from data.table:

Warning message:
In [.data.table(data, , :=(ind, NULL), with = FALSE) :
with=FALSE together with := was deprecated in v1.9.4 released Oct 2014. Please wrap the LHS of := with parentheses; e.g., DT[,(myVar):=sum(b),by=a] to assign to column name(s) held in variable myVar. See ?':=' for other examples. As warned in 2014, this is now a warning.