support/scripts/pkg-stats: fix flake8 errors

support/scripts/pkg-stats: fix flake8 errors

Fixes the following flake8 warnings:

support/scripts/pkg-stats:34:2: W605 invalid escape sequence '\$'
support/scripts/pkg-stats:34:4: W605 invalid escape sequence '\('
support/scripts/pkg-stats:34:11: W605 invalid escape sequence '\$'
support/scripts/pkg-stats:34:13: W605 invalid escape sequence '\('
support/scripts/pkg-stats:34:32: W605 invalid escape sequence '\)'
support/scripts/pkg-stats:34:34: W605 invalid escape sequence '\)'
support/scripts/pkg-stats:35:2: W605 invalid escape sequence '\s'
support/scripts/pkg-stats:35:14: W605 invalid escape sequence '\S'
support/scripts/pkg-stats:35:17: W605 invalid escape sequence '\s'
support/scripts/pkg-stats:42:1: E302 expected 2 blank lines, found 1
support/scripts/pkg-stats:587:133: E501 line too long (157 > 132 characters)

Note that the "invalid escape sequence" errors work because Python
leaves the \ in place if it doesn't recognise the escape sequence. But
it's better practice to use a raw string for regular expressions.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>