Tweak a style of titles of the system settings

src/main/twirl/gitbucket/core/admin/plugins.scala.html

@@ -5,7 +5,7 @@
     <form action="@context.path/admin/plugins/_reload" method="POST" class="pull-right">
       <input type="submit" value="Reload plugins" class="btn btn-default">
     </form>
-    <h1>Plugins</h1>
+    <h1 class="system-config-title">Plugins</h1>
     @if(plugins.size > 0) {
       <ul>
       @plugins.map { case (plugin, enabled) =>

src/main/webapp/assets/common/css/gitbucket.css

@@ -16,6 +16,11 @@ h1 {
   line-height: 32px;
 }
 
+h1.system-config-title {
+  margin-top: 0px;
+  margin-bottom: 20px;
+}
+
 h2 {
   font-size: 28px;
   line-height: 30px;