Add missing translation

public/language/en-GB/admin/extend/plugins.json

@@ -20,6 +20,7 @@
 	"plugin-item.themes": "Themes",
 	"plugin-item.deactivate": "Deactivate",
 	"plugin-item.activate": "Activate",
+	"plugin-item.install": "Install",
 	"plugin-item.uninstall": "Uninstall",
 	"plugin-item.settings": "Settings",
 	"plugin-item.installed": "Installed",
@@ -43,4 +44,4 @@
 	"alert.package-manager-unreachable": "<p>NodeBB could not reach the package manager, an upgrade is not suggested at this time.</p>",
 	"alert.incompatible": "<p>Your version of NodeBB (v%1) is only cleared to upgrade to v%2 of this plugin. Please update your NodeBB if you wish to install a newer version of this plugin.</p>",
 	"alert.possibly-incompatible": "<div class=\"alert alert-warning\"><p><strong>No Compatibility Information Found</strong></p><p>This plugin did not specify a specific version for installation given your NodeBB version. Full compatibility cannot be guaranteed, and may cause your NodeBB to no longer start properly.</p></div><p>In the event that NodeBB cannot boot properly:</p><pre><code>$ ./nodebb reset plugin=\"%1\"</code></pre><p>Continue installation of latest version of this plugin?</p>"
-}
+}