Use new plugin syntax all around

tests/test_plugin_sourcing.sh

@@ -11,7 +11,7 @@ check_binding_defined() {
 
 test_plugin_sourcing() {
 	set_tmux_conf_helper <<- HERE
-	set -g @tpm_plugins "doesnt_matter/tmux_test_plugin"
+	set -g @plugin "doesnt_matter/tmux_test_plugin"
 	run-shell "$PWD/tpm"
 	HERE
 

tests/test_plugin_update.sh

@@ -12,7 +12,7 @@ manually_install_the_plugin() {
 
 test_plugin_installation() {
 	set_tmux_conf_helper <<- HERE
-	set -g @tpm_plugins "tmux-plugins/tmux-example-plugin"
+	set -g @plugin "tmux-plugins/tmux-example-plugin"
 	run-shell "$PWD/tpm"
 	HERE
 

tpm

@@ -17,7 +17,7 @@ set_tpm_path() {
 	$CURRENT_DIR/scripts/set_tpm_path.sh >/dev/null 2>&1
 }
 
-# 1. Fetches plugin names from `@tpm_plugins` user variable.
+# 1. Fetches plugin names from `@plugin` variables
 # 2. Creates full plugin path
 # 3. Sources all *.tmux files from each of the plugin directories
 #	 - no errors raised if directory does not exist