Fix th and td selectors that override the attribute 'align'

sass/base/generic.sass

@@ -126,7 +126,8 @@ pre
 table
   td,
   th
-    text-align: left
     vertical-align: top
+    &:not([align])
+      text-align: left
   th
     color: $text-strong

sass/base/minireset.sass

@@ -81,4 +81,5 @@ table
 td,
 th
   padding: 0
-  text-align: left
+  &:not([align])
+    text-align: left

sass/elements/content.sass

@@ -125,7 +125,8 @@ $content-table-foot-cell-color: $text-strong !default
       vertical-align: top
     th
       color: $content-table-cell-heading-color
-      text-align: left
+      &:not([align])
+        text-align: left
     thead
       td,
       th

sass/elements/table.sass

@@ -53,7 +53,8 @@ $table-striped-row-even-hover-background-color: $white-ter !default
         color: currentColor
   th
     color: $table-cell-heading-color
-    text-align: left
+    &:not([align])
+      text-align: left
   tr
     &.is-selected
       background-color: $table-row-active-background-color