debian package: mark /etc/laminar.conf as a config file

This triggers apt's configuration file management system, allowing
the user to choose their locally modified version, the new upstream
version, inspect differences etc; instead of blindly overwriting it.

Resolves #92.

pkg/debian10-amd64.sh

@@ -33,6 +33,7 @@ Maintainer: Oliver Giles <web ohwg net>
 Depends: libcapnp-0.7.0, libsqlite3-0, zlib1g
 Description: Lightweight Continuous Integration Service
 EOF
+echo /etc/laminar.conf > laminar/DEBIAN/conffiles
 cat <<EOF > laminar/DEBIAN/postinst
 #!/bin/bash
 echo Creating laminar user with home in /var/lib/laminar

pkg/debian10-armhf.sh

@@ -48,6 +48,7 @@ Maintainer: Oliver Giles <web ohwg net>
 Depends: libcapnp-0.7.0, libsqlite3-0, zlib1g
 Description: Lightweight Continuous Integration Service
 EOF
+echo /etc/laminar.conf > laminar/DEBIAN/conffiles
 cat <<EOF > laminar/DEBIAN/postinst
 #!/bin/bash
 echo Creating laminar user with home in /var/lib/laminar

pkg/debian9-amd64.sh

@@ -53,6 +53,7 @@ Maintainer: Oliver Giles <web ohwg net>
 Depends: libsqlite3-0, zlib1g
 Description: Lightweight Continuous Integration Service
 EOF
+echo /etc/laminar.conf > laminar/DEBIAN/conffiles
 cat <<EOF > laminar/DEBIAN/postinst
 #!/bin/bash
 echo Creating laminar user with home in /var/lib/laminar

pkg/debian9-armhf.sh

@@ -73,6 +73,7 @@ Maintainer: Oliver Giles <web ohwg net>
 Depends: libsqlite3-0, zlib1g
 Description: Lightweight Continuous Integration Service
 EOF
+echo /etc/laminar.conf > laminar/DEBIAN/conffiles
 cat <<EOF > laminar/DEBIAN/postinst
 #!/bin/bash
 echo Creating laminar user with home in /var/lib/laminar