Fix TRANSFORM_INVALID_GROUP_CHARS deprecation warning

examples/hosts

@@ -7,5 +7,5 @@
 # For improved Ansible performance, SSH pipelining is enabled by default (`ansible_ssh_pipelining=yes`).
 # If this causes SSH connection troubles, feel free to disable it.
 
-[matrix-servers]
+[matrix_servers]
 matrix.<your-domain> ansible_host=<your-server's external IP address> ansible_ssh_user=root ansible_ssh_pipelining=yes

setup.yml

@@ -1,6 +1,6 @@
 ---
 - name: "Set up a Matrix server"
-  hosts: "{{ target if target is defined else 'matrix-servers' }}"
+  hosts: "{{ target if target is defined else 'matrix_servers' }}"
   become: true
 
   roles: