Describe the bug

The b-media components "aside" slot has a default vertical align class of align-self-top which does not exist in bootstrap CSS. I believe align-self-start is what was meant.

Steps to reproduce the bug

1. Go to https://bootstrap-vue.js.org/docs/components/media#vertical-align
2. It says possible values are top, center and end, with top as default.
3. top maps to using the align-self-top class which has no styles

Expected behavior

Replace top with start in docs and code.

Versions

Libraries:

• BootstrapVue: 2.0
• Bootstrap: 4.3
• Vue: 2.6

Environment:

N/A