bootstrap4: Removed invalid scope attribut in a tr element. (#691)

bootstrap4: Removed invalid scope attribut in a tr element.

The problem was introduced in the WIP commit
7a0518d:

diff --git a/django_tables2/templates/django_tables2/bootstrap.html b/django_tables2/templates/django_tables2/bootstrap4.html
index feaf220..6cc1487 100644
--- a/django_tables2/templates/django_tables2/bootstrap.html
+++ b/django_tables2/templates/django_tables2/bootstrap4.html
@@ -25,7 +25,7 @@
                 <tbody {{ table.attrs.tbody.as_html }}>
                 {% for row in table.paginated_rows %}
                     {% block table.tbody.row %}
-                    <tr {{ row.attrs.as_html }}>
+                    <tr scope="row" {{ row.attrs.as_html }}>
                         {% for column, cell in row.items %}
                             <td {{ column.attrs.td.as_html }}>{% if column.localize == None %}{{ cell }}{% else %}{% if column.localize %}{{ cell|localize }}{% else %}{{ cell|unlocalize }}{% endif %}{% endif %}</td>
                         {% endfor %}

django_tables2/templates/django_tables2/bootstrap4.html

@@ -25,7 +25,7 @@
                 <tbody {{ table.attrs.tbody.as_html }}>
                 {% for row in table.paginated_rows %}
                     {% block table.tbody.row %}
-                    <tr scope="row" {{ row.attrs.as_html }}>
+                    <tr {{ row.attrs.as_html }}>
                         {% for column, cell in row.items %}
                             <td {{ column.attrs.td.as_html }}>{% if column.localize == None %}{{ cell }}{% else %}{% if column.localize %}{{ cell|localize }}{% else %}{{ cell|unlocalize }}{% endif %}{% endif %}</td>
                         {% endfor %}