Convert fetch-indexes to Bash.

fetch-indexes

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/bin/bash
 # download current package indexes to data/<series>{,-proposed}/ for running
 # britney against a PPA. The PPA will play the role of "-proposed" (i. e.
 # "unstable" in britney terms, containing the updated packages to test), the
@@ -23,7 +23,7 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
-. config.sh
+source config.sh
 
 set -u