minor symfony#13259 [3.4] Updated links to Bootstrap docs (skmedix)

This PR was merged into the 3.4 branch.

Discussion
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[3.4] Updated links to Bootstrap docs

This is a follow up of symfony#13253 for 3.4

Commits
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2f99a03 👽 Updated links to Bootstrap docs

Author: OskarStark

form/bootstrap4.rst

@@ -12,10 +12,10 @@ template which other templates extend from):
 
     {# beware that the blocks in your template may be named different #}
     {% block head_css %}
-        <!-- Copy CSS from https://getbootstrap.com/docs/4.1/getting-started/introduction/#css -->
+        <!-- Copy CSS from https://getbootstrap.com/docs/4.4/getting-started/introduction/#css -->
     {% endblock %}
     {% block head_js %}
-        <!-- Copy JavaScript from https://getbootstrap.com/docs/4.1/getting-started/introduction/#js -->
+        <!-- Copy JavaScript from https://getbootstrap.com/docs/4.4/getting-started/introduction/#js -->
     {% endblock %}
 
 If your application uses modern front-end practices, it's better to use
@@ -112,4 +112,4 @@ is a strong connection between the error and its ``<input>``, as required by the
 `WCAG 2.0 standard`_.
 
 .. _`WCAG 2.0 standard`: https://www.w3.org/TR/WCAG20/
-.. _`custom forms`: https://getbootstrap.com/docs/4.1/components/forms/#custom-forms
+.. _`custom forms`: https://getbootstrap.com/docs/4.4/components/forms/#custom-forms

form/form_customization.rst

@@ -856,7 +856,7 @@ more details about this concept in Twig, see :ref:`twig-reference-form-variables
 .. _`bootstrap_3_horizontal_layout.html.twig`: https://github.com/symfony/symfony/blob/master/src/Symfony/Bridge/Twig/Resources/views/Form/bootstrap_3_horizontal_layout.html.twig
 .. _`bootstrap_4_layout.html.twig`: https://github.com/symfony/symfony/blob/master/src/Symfony/Bridge/Twig/Resources/views/Form/bootstrap_4_layout.html.twig
 .. _`bootstrap_4_horizontal_layout.html.twig`: https://github.com/symfony/symfony/blob/master/src/Symfony/Bridge/Twig/Resources/views/Form/bootstrap_4_horizontal_layout.html.twig
-.. _`Bootstrap 3 CSS framework`: https://getbootstrap.com/docs/3.3/
-.. _`Bootstrap 4 CSS framework`: https://getbootstrap.com/docs/4.1/
+.. _`Bootstrap 3 CSS framework`: https://getbootstrap.com/docs/3.4/
+.. _`Bootstrap 4 CSS framework`: https://getbootstrap.com/docs/4.4/
 .. _`foundation_5_layout.html.twig`: https://github.com/symfony/symfony/blob/master/src/Symfony/Bridge/Twig/Resources/views/Form/foundation_5_layout.html.twig
 .. _`Foundation CSS framework`: http://foundation.zurb.com/