fix: mail link color (#1812)

api/templates/invite_member_mail_template_en-US.html

@@ -60,7 +60,7 @@
             <p>Dear {{ to }},</p>
             <p>{{ inviter_name }} is pleased to invite you to join our workspace on Dify, a platform specifically designed for LLM application development. On Dify, you can explore, create, and collaborate to build and operate AI applications.</p>
             <p>You can now log in to Dify using the GitHub or Google account associated with this email.</p>
-            <p style="text-align: center;"><a class="button" href="{{ url }}">Login Here</a></p>
+            <p style="text-align: center;"><a style="color: #fff; text-decoration: none" class="button" href="{{ url }}">Login Here</a></p>
         </div>
         <div class="footer">
             <p>Best regards,</p>

api/templates/invite_member_mail_template_zh-CN.html

@@ -60,7 +60,7 @@
             <p>尊敬的 {{ to }}，</p>
             <p>{{ inviter_name }} 现邀请您加入我们在 Dify 的工作区，这是一个专为 LLM 应用开发而设计的平台。在 Dify 上，您可以探索、创造和合作，构建和运营 AI 应用。</p>
             <p>您现在可以使用与此邮件相对应的 GitHub 或 Google 账号登录 Dify。</p>
-            <p style="text-align: center;"><a class="button" href="{{ url }}">在此登录</a></p>
+            <p style="text-align: center;"><a style="color: #fff; text-decoration: none" class="button" href="{{ url }}">在此登录</a></p>
         </div>
         <div class="footer">
             <p>此致，</p>