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

reader/atom/atom_10_test.go

@@ -303,6 +303,16 @@ func TestParseEntryWithHTMLTitle(t *testing.T) {
 		<summary>Some text.</summary>
 	  </entry>
 
+	  <entry>
+		<title>
+			<![CDATA[Entry title with space around CDATA]]>
+		</title>
+		<link href="http://example.org/2003/12/13/atom03"/>
+		<id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
+		<updated>2003-12-13T18:30:02Z</updated>
+		<summary>Some text.</summary>
+	  </entry>
+
 	</feed>`
 
 	feed, err := Parse("https://example.org/", bytes.NewBufferString(data))
@@ -317,6 +327,10 @@ func TestParseEntryWithHTMLTitle(t *testing.T) {
 	if feed.Entries[1].Title != "Test “Test”" {
 		t.Errorf("Incorrect entry title, got: %q", feed.Entries[1].Title)
 	}
+
+	if feed.Entries[2].Title != "Entry title with space around CDATA" {
+		t.Errorf("Incorrect entry title, got: %q", feed.Entries[2].Title)
+	}
 }
 
 func TestParseEntryWithXHTMLTitle(t *testing.T) {