Remove trailing spaces.

Author: XhmikosR

docs/4.0/components/forms.md

@@ -928,7 +928,7 @@ Our example forms show native textual `<input>`s above, but form validation styl
   <div class="custom-file">
     <input type="file" class="custom-file-input" id="validatedCustomFile" required>
     <label class="custom-file-label" for="validatedCustomFile">Choose file...</label>
-    <div class="invalid-feedback">Example invalid custom file feedback</div>  
+    <div class="invalid-feedback">Example invalid custom file feedback</div>
   </div>
 </form>
 {% endexample %}