fix: styles for ion-slides migration (#2930)

Author: sean-perkins

docs/angular/slides.md

@@ -109,6 +109,7 @@ swiper-slide {
   display: flex;
   position: relative;
 
+  flex-direction: column;
   flex-shrink: 0;
   align-items: center;
   justify-content: center;

versioned_docs/version-v6/angular/slides.md

@@ -107,6 +107,7 @@ swiper-slide {
   display: flex;
   position: relative;
 
+  flex-direction: column;
   flex-shrink: 0;
   align-items: center;
   justify-content: center;