debian/control: add ca-certificates as build dependency

debian/control

@@ -10,7 +10,8 @@ Build-Depends: debhelper (>= 9),
     golang-github-gokyle-hotp-dev,
     golang-github-mattn-go-sqlite3-dev,
     postgresql,
-    pamtester, libpam-wrapper, oathtool, xxd
+    pamtester, libpam-wrapper, oathtool, xxd,
+    ca-certificates
 Standards-Version: 3.9.8
 Section: admin
 Homepage: https://gitlab.cs.fau.de/icipguru/goatherd