[css-animations] Fix description of iterations since iteration-count can be < 1

Based on estelle@f34c9d5

Author: estelle

css-animations/Overview.bs

@@ -194,7 +194,7 @@ Keyframes</h2>
 
 	Keyframes are used to specify the values for the animating properties at various points
 	during the animation. The keyframes specify the behavior of one cycle of the animation;
-	the animation may iterate one or more times.
+	the animation may iterate zero or more times.
 
 	Keyframes are specified using a specialized CSS at-rule. A <dfn>@keyframes</dfn> rule consists of the
 	keyword "@keyframes", followed by an identifier giving a name for the animation (which will

css-animations/Overview.html

@@ -341,7 +341,7 @@ <h2 class="heading settled" data-level="3" id="animations"><span class="secno">3
    <h2 class="heading settled" data-level="4" id="keyframes"><span class="secno">4. </span><span class="content"> Keyframes</span><a class="self-link" href="#keyframes"></a></h2>
    <p>Keyframes are used to specify the values for the animating properties at various points
 	during the animation. The keyframes specify the behavior of one cycle of the animation;
-	the animation may iterate one or more times.</p>
+	the animation may iterate zero or more times.</p>
    <p>Keyframes are specified using a specialized CSS at-rule. A <dfn class="css" data-dfn-type="at-rule" data-export="" id="at-ruledef-keyframes">@keyframes<a class="self-link" href="#at-ruledef-keyframes"></a></dfn> rule consists of the
 	keyword "@keyframes", followed by an identifier giving a name for the animation (which will
 	be referenced using <a class="property" data-link-type="propdesc" href="#propdef-animation-name">animation-name</a>), followed by a set of style rules (delimited by curly