fixup doc comments

Author: ethomson

LibGit2Sharp/Core/Proxy.cs

@@ -3472,6 +3472,7 @@ public static void git_libgit2_opts_set_user_agent(string userAgent)
         /// <returns>
         /// The user-agent string.
         /// </returns>
+        /// </summary>
         public static string git_libgit2_opts_get_user_agent()
         {
             string userAgent;

LibGit2Sharp/GlobalSettings.cs

@@ -525,6 +525,7 @@ public static void SetUserAgent(string userAgent)
         /// <returns>
         /// The user-agent string.
         /// </returns>
+        /// </summary>
         public static string GetUserAgent()
         {
             return Proxy.git_libgit2_opts_get_user_agent();