chore: enable Markdownlint rule MD003/heading-style (apache#3314)

.markdownlint.yml

@@ -16,7 +16,6 @@
 #
 
 MD001: false
-MD003: false
 MD004: false
 MD005: false
 MD006: false

doc/install-dependencies.md

@@ -27,17 +27,15 @@
 - [Debian 9 & 10](#debian-9--10)
 - [Mac OSX](#mac-osx)
 
-Note
-====
+# Note
 
 - Since v2.0 Apache APISIX would not support the v2 protocol storage to etcd anymore, and the minimum etcd version supported is v3.4.0. What's more, etcd v3 uses gRPC as the messaging protocol, while Apache APISIX uses HTTP(S) to communicate with etcd cluster, so be sure the [etcd gRPC gateway](https://etcd.io/docs/v3.4.0/dev-guide/api_grpc_gateway/) is enabled.
 
 - Now by default Apache APISIX uses HTTP protocol to talk with etcd cluster, which is insecure. Please configure certificate and corresponding private key for your etcd cluster, and use "https" scheme explicitly in the etcd endpoints list in your Apache APISIX configuration, if you want to keep the data secure and integral. See the etcd section in `conf/config-default.yaml` for more details.
 
 - If you want use Tengine instead of OpenResty, please take a look at this installation step script [Install Tengine at Ubuntu](../.travis/linux_tengine_runner.sh).
 
-CentOS 7
-========
+# CentOS 7
 
 ```shell
 # install epel, `luarocks` need it.
@@ -61,8 +59,7 @@ sudo yum install -y openresty curl git gcc luarocks lua-devel
 nohup etcd &
 ```
 
-Fedora 31 & 32
-==============
+# Fedora 31 & 32
 
 ```shell
 # add OpenResty source
@@ -82,8 +79,7 @@ sudo yum install -y openresty curl git gcc luarocks lua-devel
 nohup etcd &
 ```
 
-Ubuntu 16.04 & 18.04
-====================
+# Ubuntu 16.04 & 18.04
 
 ```shell
 # add OpenResty source
@@ -106,8 +102,7 @@ sudo apt-get install -y git openresty curl luarocks
 nohup etcd &
 ```
 
-Debian 9 & 10
-=============
+# Debian 9 & 10
 
 ```shell
 # optional
@@ -135,8 +130,7 @@ sudo apt-get install -y git openresty curl luarocks make
 nohup etcd &
 ```
 
-Mac OSX
-=======
+# Mac OSX
 
 ```shell
 # install OpenResty, etcd and some compilation tools

doc/zh-cn/install-dependencies.md

@@ -26,17 +26,15 @@
 - [Debian 9 & 10](#debian-9--10)
 - [Mac OSX](#mac-osx)
 
-注意
-====
+# 注意
 
 - Apache APISIX 从 v2.0 开始不再支持 `v2` 版本的 etcd，并且 etcd 最低支持版本为 v3.4.0，因此请使用 etcd 3.4.0+。更重要的是，因为 etcd v3 使用 gPRC 作为消息传递协议，而 Apache APISIX 使用 HTTP(S) 与 etcd 集群通信，因此请确保启用 [etcd gRPC gateway](https://etcd.io/docs/v3.4.0/dev-guide/api_grpc_gateway/) 功能。
 
 - 目前 Apache APISIX 默认使用 HTTP 协议与 etcd 集群通信，这并不安全，如果希望保障数据的安全性和完整性。 请为您的 etcd 集群配置证书及对应私钥，并在您的 Apache APISIX etcd endpoints 配置列表中明确使用 `https` 协议前缀。请查阅 `conf/config-default.yaml` 中 etcd 一节相关的配置来了解更多细节。
 
 - 如果你要想使用 Tengine 替代 OpenResty，请参考 [Install Tengine at Ubuntu](../../.travis/linux_tengine_runner.sh)。
 
-CentOS 7
-========
+# CentOS 7
 
 ```shell
 # 安装 epel, `luarocks` 需要它
@@ -60,8 +58,7 @@ sudo yum install -y openresty curl git gcc luarocks lua-devel
 nohup etcd &
 ```
 
-Fedora 31 & 32
-==============
+# Fedora 31 & 32
 
 ```shell
 # 添加 OpenResty 源
@@ -81,8 +78,7 @@ sudo yum install -y openresty curl git gcc luarocks lua-devel
 nohup etcd &
 ```
 
-Ubuntu 16.04 & 18.04
-====================
+# Ubuntu 16.04 & 18.04
 
 ```shell
 # 添加 OpenResty 源
@@ -105,8 +101,7 @@ sudo apt-get install -y git openresty curl luarocks
 nohup etcd &
 ```
 
-Debian 9 & 10
-=============
+# Debian 9 & 10
 
 ```shell
 # 可选
@@ -134,8 +129,7 @@ sudo apt-get install -y git openresty curl luarocks
 nohup etcd &
 ```
 
-Mac OSX
-=======
+# Mac OSX
 
 ```shell
 # 安装 OpenResty, etcd 和 编译工具