doc/ffprobe.xsd: specify tag elements in stream after disposition element

Fix XML schema validation, since elements must appear in the same order
as specified in the schema.

doc/ffprobe.xsd

@@ -103,8 +103,8 @@
 
     <xsd:complexType name="streamType">
       <xsd:sequence>
-        <xsd:element name="tag" type="ffprobe:tagType" minOccurs="0" maxOccurs="unbounded"/>
         <xsd:element name="disposition" type="ffprobe:streamDispositionType" minOccurs="0" maxOccurs="1"/>
+        <xsd:element name="tag" type="ffprobe:tagType" minOccurs="0" maxOccurs="unbounded"/>
       </xsd:sequence>
 
       <xsd:attribute name="index"            type="xsd:int" use="required"/>