cyclocomp_linter() message should be customized to 'function'/'expression'

[MichaelChirico]

cyclocomp() can measure complexity of functions or expressions, but the message always says "function":

lintr/R/cyclocomp_linter.R

Line 48 in 5bc4dbe

"Reduce the cyclomatic complexity of this function from %d to at most %d.",

This might be confusing if the lint hits a non-function expression:

lint(linters = cyclocomp_linter(5L), "
for (i in 1:10)
  for (j in 1:10)
    for (k in 1:10)
      i*j*k
")
# <text>:2:1: style: [cyclocomp_linter] Reduce the cyclomatic complexity of this function from 10 to at most 5.
# for (i in 1:10)
# ^