Fixes #1552 > .container.is-fluid margins (#1608)

Changing the default behaviour of `.is-fluid` container: removing media breakpoint from the rule, so the behaviour is consistent with described in docs:
```
This container is fluid: it will have a 32px gap on either side, on any viewport size.
```

sass/elements/container.sass

@@ -5,12 +5,13 @@ $container-offset: (2 * $gap) !default
   margin: 0 auto
   position: relative
   width: auto
+  &.is-fluid
+    margin-left: $gap
+    margin-right: $gap
+    max-width: none
+    width: auto
   +desktop
     max-width: $desktop - $container-offset
-    &.is-fluid
-      margin-left: $gap
-      margin-right: $gap
-      max-width: none
   +until-widescreen
     &.is-widescreen
       max-width: $widescreen - $container-offset