Handle atom feed with space around CDATA

Trim space around CDATA elements before extracting the CharData.

This problem was discovered when reading https://www.sethvargo.com/feed.xml.
Title and Summary fields have newlines and space between the <title>
element and the CDATA element. e.g.

  <title>
    <![CDATA[Entry title here]]>
  </title>

This meant the title of the feed was coming into MiniFlux as,
  <![CDATA[Entry title here]]>

reader/atom/atom_10.go

@@ -229,10 +229,9 @@ type atom10Text struct {
 
 func (a *atom10Text) String() string {
 	var content string
-
 	switch {
 	case a.Type == "", a.Type == "text", a.Type == "text/plain":
-		if strings.HasPrefix(a.InnerXML, `<![CDATA[`) {
+		if strings.HasPrefix(strings.TrimSpace(a.InnerXML), `<![CDATA[`) {
 			content = html.EscapeString(a.CharData)
 		} else {
 			content = a.InnerXML