[css-multicol] Rename tracks to columns

In the Pseudo-algorithm section, mention is made of tracks, terminology not used anywhere else in the spec. Updated this to columns as per WG resolution.

Fixes #3649

Author: rachelandrew

css-multicol-1/Overview.bs

@@ -586,7 +586,7 @@ Two assumptions are being made by the pseudo-algorithm:
 	(11)  W := max(0, ((U + column-gap)/N - column-gap))
 	</pre>
 
-	For the purpose of finding the number of auto-repeated tracks, the UA must floor the track size to a UA-specified value to avoid division by zero. It is suggested that this floor be 1px or less.
+	For the purpose of finding the number of auto-repeated columns, the UA must floor the column size to a UA-specified value to avoid division by zero. It is suggested that this floor be 1px or less.
 
 	In fragmented contexts such as in paged media, user agents may perform this calculation on a
 	per-fragment basis.
@@ -1416,8 +1416,13 @@ Pagination and overflow outside multicol containers</h3>
 
 This appendix is <em>informative</em>.
 
-<h3 id="changes-from-20171005">Changes from the <a href="https://www.w3.org/TR/2017/WD-css-multicol-1-20171005/">Working Draft (WD) of 5 October 2017</a></h3>
+<h3 id="changes-from-20171005">Changes from the <a href="https://www.w3.org/TR/2018/WD-css-multicol-1-20180528/">Working Draft (WD) of 28 May 2018</a></h3>
 <ul>
+	<li>Changed the sentence added in the pseudo-algorithm section after the 7 Jan 2016 resolution, to refer to <em>columns</em> and not <em>tracks</em> as tracks are not defined in this specification. Resolved <a href="https://github.com/w3c/csswg-drafts/issues/3649#issuecomment-472505520">13 March 2019</a>.</li>
+	<li>Changes and clarifications to the SVG images used in the specification.</li>
+</ul>
+
+<h3 id="changes-from-20171005">Changes from the <a href="https://www.w3.org/TR/2017/WD-css-multicol-1-20171005/">Working Draft (WD) of 5 October 2017</a></h3>
 	<li>Changed references to paged media to refer to fragmented contexts. Resolved <a href="https://github.com/w3c/csswg-drafts/issues/1746#issuecomment-380731574">12 Apr 2018</a>.</li>
 	<li>Changed a line regarding the <code>column-fill</code> property:
 	<br><q>In continuous media, this property does not have any effect in