Remove hard-coded Perl path that causes email fetching to fail.

When a user installs a local Perl version to run MisterHouse
under instead of using the system-provided Perl, then the
hardcoded Perl path at the shebang in get_email causes the
module search path to be incorrect. /usr/bin/env perl
properly solves this issue.
Merge pull request #249 from hollie/fix_get_email

Fix get email for non-system-wide Perl installations