feat: drop support for unsupported Debian and Ubuntu releases

While the latest packages may continue to work on other releases, we will no longer officially support these releases, nor will we distribute packages.

docs/getting-started/install/dreamhost.md

@@ -19,7 +19,7 @@ source openrc.sh # Set the environment variables for DreamHost Cloud
 
 This allows OpenStack client to connect to DreamHost API endpoints.
 The command below creates a new server instance named `my-dokku-instance`
-based on Ubuntu 14.04, with 2 GB RAM and 1 CPU (the flavor called
+based on Ubuntu 18.04, with 2 GB RAM and 1 CPU (the flavor called
 `supersonic`), opening network port access to HTTP and SSH (the
 `default` security group), and the name of the chosen SSH key. This
 key will be automatically added to the new server in the
@@ -28,7 +28,7 @@ be reused by Dokku.
 
 ```sh
 openstack server create \
-  --image Ubuntu-14.04 \
+  --image Ubuntu-18.04 \
   --flavor gp1.supersonic \
   --security-group default \
   --key-name $YOUR_SSH_KEYNAME \
@@ -46,7 +46,7 @@ server:
 apt_upgrade: true
 
 apt_sources:
- - source: "deb https://packagecloud.io/dokku/dokku/ubuntu/ trusty main"
+ - source: "deb https://packagecloud.io/dokku/dokku/ubuntu/ bionic main"
    key: |
     -----BEGIN PGP PUBLIC KEY BLOCK-----
     Version: SKS 1.1.5
@@ -107,7 +107,7 @@ apt_sources:
     =H60S
     -----END PGP PUBLIC KEY BLOCK-----
    filename: dokku.list
- - source: "deb https://apt.dockerproject.org/repo ubuntu-trusty main"
+ - source: "deb https://apt.dockerproject.org/repo ubuntu-bionic main"
    key: |
     -----BEGIN PGP PUBLIC KEY BLOCK-----
     Version: SKS 1.1.5