fix(welcome-mat): Fix content vertical centering in IE11 (#3631) (#3638)

* fix/welcome-mat: add style to vertically center content in IE11
* fix/welcome-mat: update release notes

Author: Dottenpixel

RELEASENOTES.md

@@ -309,6 +309,8 @@
 - Moved `slds-grid` from `slds-modal__content` to `slds-welcome-mat__content`
 #### Deprecated
 - Deprecated `.slds-welcome-mat .slds-modal-container` selector for `.slds-modal-small` to be applied to `slds-modal`. To upgrade existing welcome mat, in `slds-modal`, replace `slds-welcome-mat` with `slds-modal_small`, and also remove `slds-welcome-mat__content` from `slds-modal-container`. Markup structure changes need to be made existing code. First, wrap the existing content of `<div class='slds-modal-container'>` with `<div class='slds-welcome-mat__content slds-grid'>`. Then, wrap `<div class='slds-welcome-mat__content slds-grid'>` with `<div class='slds-welcome-mat'>`.
+#### Fixed
+- Fixed vertical alignment of `slds-welcome-mat__info-content` in IE11.
 
 ## Utilities
 

ui/components/welcome-mat/RELEASENOTES.md

@@ -22,6 +22,9 @@
 ### Deprecated
 - Deprecated `.slds-welcome-mat .slds-modal-container` selector for `.slds-modal-small` to be applied to `slds-modal`. To upgrade existing welcome mat, in `slds-modal`, replace `slds-welcome-mat` with `slds-modal_small`, and also remove `slds-welcome-mat__content` from `slds-modal-container`. Markup structure changes need to be made existing code. First, wrap the existing content of `<div class='slds-modal-container'>` with `<div class='slds-welcome-mat__content slds-grid'>`. Then, wrap `<div class='slds-welcome-mat__content slds-grid'>` with `<div class='slds-welcome-mat'>`.
 
+### Fixed
+- Fixed vertical alignment of `slds-welcome-mat__info-content` in IE11.
+
 ## 2.7.0
 
 ### Changed

ui/components/welcome-mat/base/_index.scss

@@ -57,6 +57,7 @@
   background-repeat: no-repeat;
   background-size: contain;
   background-color: $welcome-mat-background-color-info;
+  align-items: center;
 }
 
 /**