Validate sourcecode by w3c validator (#100)

* validate sourcecode by w3c validator
  * https://validator.w3.org/#validate_by_input
* rename duplicate `#navbarNav0`

Author: m5o

src/html/headers/headers-03.html

@@ -1,11 +1,11 @@
 <header>
   <div class="container">
     <nav class="navbar navbar-expand-md">
-      <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarNav0" aria-controls="navbarNav0" aria-expanded="false" aria-label="Toggle navigation">
+      <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbar-example-03" aria-controls="navbar-example-03" aria-expanded="false" aria-label="Toggle navigation">
         <span class="navbar-toggler-icon"></span>
       </button>
 
-      <div class="collapse navbar-collapse" id="navbarNav0">
+      <div class="collapse navbar-collapse" id="navbar-example-03">
         <ul class="navbar-nav mr-auto ml-auto">
           <li class="nav-item active">
             <a class="nav-link" href="https://www.froala.com">Home <span class="sr-only">(current)</span></a>

src/html/headers/headers-09.html

@@ -7,11 +7,11 @@
         </a>
       </div>
 
-      <button class="navbar-toggler" type="button" data-toggle="collapse" data-target=".navbar-collapse-1" aria-controls="navbarNav6" aria-expanded="false" aria-label="Toggle navigation">
+      <button class="navbar-toggler" type="button" data-toggle="collapse" data-target=".navbar-example-09" aria-controls="navbar-example-09" aria-expanded="false" aria-label="Toggle navigation">
         <span class="navbar-toggler-icon"></span>
       </button>
 
-      <div class="collapse navbar-collapse justify-content-center col-md-8 navbar-collapse-1">
+      <div class="collapse navbar-collapse justify-content-center col-md-8 navbar-example-09">
         <ul class="navbar-nav justify-content-center">
           <li class="nav-item active">
             <a class="nav-link" href="https://www.froala.com">Home <span class="sr-only">(current)</span></a>
@@ -31,7 +31,7 @@
         </ul>
       </div>
 
-      <div class="collapse navbar-collapse justify-content-end col-md-2 navbar-collapse-1">
+      <div class="collapse navbar-collapse justify-content-end col-md-2 navbar-example-09">
         <ul class="navbar-nav">
           <li class="nav-item">
             <a class="nav-link" href="https://www.froala.com">Log In <i class="fas fa-sign-in-alt"></i></a>