Build against the 3.28 runtime for now

Freedesktop 18.08.11 dropped openssl 1.0 which caused hyper to
no longer build. Reverting to the old runtime till hyper is
upgraded. See #84 for more.

org.gnome.PodcastsDevel.json

@@ -1,7 +1,7 @@
 {
     "app-id" : "org.gnome.PodcastsDevel",
     "runtime" : "org.gnome.Platform",
-    "runtime-version" : "master",
+    "runtime-version" : "3.28",
     "sdk" : "org.gnome.Sdk",
     "sdk-extensions" : [
         "org.freedesktop.Sdk.Extension.rust-stable"
@@ -30,6 +30,7 @@
         ],
         "env" : {
             "CARGO_HOME" : "/run/build/Podcasts/cargo",
+            /* "RUSTFLAGS" : "--error-format=short", */
             "RUST_BACKTRACE" : "1"
         }
     },