docs: ✏️ just tweak demo

Author: ttskch

docs/index.html

@@ -33,6 +33,7 @@ <h3>Example of <a href="https://github.com/ttskch/select2-bootstrap4-theme" targ
         <option>5</option>
       </select>
     </div>
+
     <div class="form-group">
       <label>Example of multiple select</label>
       <select multiple data-placeholder="Choose anything" data-allow-clear="1">
@@ -58,11 +59,13 @@ <h3>Example of <a href="https://github.com/ttskch/select2-bootstrap4-theme" targ
         <option>Pennie Khang</option>
       </select>
     </div>
+
     <div class="form-group">
       <label>Example of disabled select</label>
       <select disabled data-placeholder="Cannot choose" data-allow-clear="1">
       </select>
     </div>
+
     <div class="form-group">
       <label>Example of select with optgroup</label>
       <select data-placeholder="Choose one thing" data-allow-clear="1">
@@ -79,21 +82,22 @@ <h3>Example of <a href="https://github.com/ttskch/select2-bootstrap4-theme" targ
         </optgroup>
       </select>
     </div>
+
     <div class="form-group">
       <label>Example of input-group</label>
       <div class="input-group">
         <div class="input-group-prepend">
           <span class="input-group-text">Prepend</span>
         </div>
-        <select data-placeholder="Choose on thing" data-allow-clear="1">
+        <select data-placeholder="Choose one thing" data-allow-clear="1">
           <option></option>
           <option>1</option>
           <option>2</option>
           <option>3</option>
         </select>
       </div>
       <div class="input-group mt-2">
-        <select data-placeholder="Choose on thing" data-allow-clear="1">
+        <select data-placeholder="Choose one thing" data-allow-clear="1">
           <option></option>
           <option>1</option>
           <option>2</option>
@@ -107,7 +111,7 @@ <h3>Example of <a href="https://github.com/ttskch/select2-bootstrap4-theme" targ
         <div class="input-group-prepend">
           <span class="input-group-text">Prepend</span>
         </div>
-        <select data-placeholder="Choose on thing" data-allow-clear="1">
+        <select data-placeholder="Choose one thing" data-allow-clear="1">
           <option></option>
           <option>1</option>
           <option>2</option>
@@ -118,6 +122,7 @@ <h3>Example of <a href="https://github.com/ttskch/select2-bootstrap4-theme" targ
         </div>
       </div>
     </div>
+
     <div class="form-group">
       <label>Example of validated select</label>
       <select data-placeholder="Invalid example" class="form-control is-invalid" data-allow-clear="1">