Fix loading of mounted secret files to env variables (#14)

* Don't require `SECRETS_PATH` to end with a slash

* Recurse over the secret files directory to find files [Closes #13]

lib/on_container/load_env_secrets.rb

@@ -12,10 +12,10 @@
 
 # Process only a known list of env vars that can filled by reading a file (i.e.
 # a docker secret):
-Dir["#{ENV.fetch('SECRETS_PATH', '/run/secrets/')}*"].each do |secret_filepath|
-  next unless File.file?(secret_filepath)
-
-  secret_envvarname = File.basename(secret_filepath, '.*').upcase
+Dir["#{ENV.fetch('SECRETS_PATH', '/run/secrets')}/**/*"].map do |path|
+  Pathname.new(path)
+end.select(&:file?).each do |secret_filepath|
+  secret_envvarname = secret_filepath.basename('.*').to_s.upcase
 
   # Skip if variable is already set - already-set variables have precedence over
   # the secret files:
@@ -55,4 +55,4 @@
   ENV[url_key] = uri.to_s
 end
 
-# STDERR.puts ENV.inspect
+# STDERR.puts ENV.inspect