docs(clang): fix doc for clang std

docs/_posts/2019-05-10-use-vim-as-a-c-cpp-ide.md

@@ -94,7 +94,7 @@ If you want to use `c11`, you can change `clang_std` option to:
 ```toml
 [[layers]]
   name = "lang#c"
-  [layer.clang_std]
+  [layers.clang_std]
     cpp = "c11"
 ```
 

docs/_posts/2019-05-11-use-vim-as-a-c-cpp-ide.md

@@ -127,7 +127,7 @@ C/C++ 代码格式化，主要依赖 `format` 模块，快捷键为 `SPC b f`，
 ```toml
 [[layers]]
   name = "lang#c"
-  [layer.clang_std]
+  [layers.clang_std]
     cpp = "c11"
 ```
 

docs/cn/layers/lang/c.md

@@ -73,7 +73,7 @@ lang: zh
 [[layers]]
   name = "lang#c"
   clang_executable = "/usr/bin/clang"
-  [layer.clang_std]
+  [layers.clang_std]
     c = "c11"
     cpp = "c++1z"
     objc = "c11"

docs/layers/lang/c.md

@@ -84,7 +84,7 @@ Here is an example how to use above options:
   name = "lang#c"
   clang_executable = "/usr/bin/clang"
   clang_flag = ['-I/usr/include']
-  [layer.clang_std]
+  [layers.clang_std]
     c = "c11"
     cpp = "c++1z"
     objc = "c11"