Prevent TGMPA notice showing on WP core update pages.

Prevents core/plugin/theme updates screens looking like:

![screenshot](http://snag.gy/mIFC6.jpg)

Author: jrfnl

class-tgm-plugin-activation.php

@@ -1001,7 +1001,7 @@ protected function activate_single_plugin( $file_path, $slug, $automatic = false
 		 */
 		public function notices() {
 			// Remove nag on the install page / Return early if the nag message has been dismissed or user < author.
-			if ( $this->is_tgmpa_page() || get_user_meta( get_current_user_id(), 'tgmpa_dismissed_notice_' . $this->id, true ) || ! current_user_can( apply_filters( 'tgmpa_show_admin_notice_capability', 'publish_posts' ) ) ) {
+			if ( ( $this->is_tgmpa_page() || $this->is_core_update_page() ) || get_user_meta( get_current_user_id(), 'tgmpa_dismissed_notice_' . $this->id, true ) || ! current_user_can( apply_filters( 'tgmpa_show_admin_notice_capability', 'publish_posts' ) ) ) {
 				return;
 			}
 
@@ -1600,6 +1600,35 @@ protected function is_tgmpa_page() {
 			return isset( $_GET['page'] ) && $this->menu === $_GET['page'];
 		}
 
+		/**
+		 * Determine if we're on a WP Core installation/upgrade page.
+		 *
+		 * @since 2.x.x
+		 *
+		 * @return boolean True when on a WP Core installation/upgrade page, false otherwise.
+		 */
+		protected function is_core_update_page() {
+			// Current screen is not always available, most notably on the customizer screen.
+			if ( ! function_exists( 'get_current_screen' ) ) {
+				return false;
+			}
+
+			$screen = get_current_screen();
+
+			if ( 'update-core' === $screen->base ) {
+				// Core update screen.
+				return true;
+			} elseif ( 'plugins' === $screen->base && isset( $_POST['action'] ) ) { // WPCS: CSRF ok.
+				// Plugins bulk update screen.
+				return true;
+			} elseif ( 'update' === $screen->base && isset( $_POST['action'] ) ) { // WPCS: CSRF ok.
+				// Individual updates (ajax call).
+				return true;
+			}
+
+			return false;
+		}
+
 		/**
 		 * Retrieve the URL to the TGMPA Install page.
 		 *