fix: use correct flag in dockerfile (#18)

Update the Dockerfile entrypoint script to use the correct version flag
syntax. The flag now requires two dashes instead of one. The syntax for
the texfile collector has also change, and the script was updated
accordingly.
Fix incorrect order of variable assignment when parsing CLI flags.

docker/run.sh

@@ -1,20 +1,21 @@
 #/bin/sh
 
 # Print version to logs for debugging purposes
-/app/fail2ban-prometheus-exporter -version
+/app/fail2ban-prometheus-exporter --version
 
 socket_path=/var/run/fail2ban/fail2ban.sock
 textfile_dir=/app/textfile/
 textfile_enabled=false
 
-# Enable textfile metrics if the folder exists (i.e. was mounted by docker)
-if [ -d $textfile_dir ]; then
-    textfile_enabled=true
-fi
-
 # Start the exporter (use exec to support graceful shutdown)
 # Inspired by: https://akomljen.com/stopping-docker-containers-gracefully/
-exec /app/fail2ban-prometheus-exporter \
-    --socket "$socket_path" \
-    --collector.textfile=$textfile_enabled \
-    --collector.textfile.directory="$textfile_dir"
+# Enable textfile metrics if the folder exists (i.e. was mounted by docker)
+if [ -d $textfile_dir ]; then
+  exec /app/fail2ban-prometheus-exporter \
+      --socket "$socket_path" \
+      --collector.textfile \
+      --collector.textfile.directory "$textfile_dir"
+else
+  exec /app/fail2ban-prometheus-exporter \
+      --socket "$socket_path"
+fi