Fix CDATA issue

Resolves #168

Sources/XMLCoder/Auxiliaries/Box/KeyedBox.swift

@@ -24,7 +24,7 @@ struct KeyedBox {
     }
 
     var value: SimpleBox? {
-        return elements[""].first as? SimpleBox
+        return elements.values.first as? SimpleBox
     }
 }
 

Sources/XMLCoder/Auxiliaries/KeyedStorage.swift

@@ -24,6 +24,10 @@ struct KeyedStorage<Key: Hashable & Comparable, Value> {
         return buffer.map { $0.0 }
     }
 
+    var values: [Value] {
+        return buffer.map { $0.1 }
+    }
+
     init<S>(_ sequence: S) where S: Sequence, S.Element == (Key, Value) {
         buffer = Buffer()
         keyMap = KeyMap()

Tests/XMLCoderTests/CDATATest.swift

@@ -0,0 +1,28 @@
+//
+//  Created by Max Desiatov on 09/04/2020.
+//
+
+import XCTest
+import XMLCoder
+
+private struct Container: Codable, Equatable {
+    let value: Int
+    let data: String
+}
+
+private let xml =
+    """
+    <container>
+       <value>42</value>
+       <data><![CDATA[lorem ipsum]]></data>
+    </container>
+    """.data(using: .utf8)!
+
+final class CDATATest: XCTestCase {
+    func testXML() throws {
+        let decoder = XMLDecoder()
+        let result = try decoder.decode(Container.self, from: xml)
+
+        XCTAssertEqual(result, Container(value: 42, data: "lorem ipsum"))
+    }
+}