Add CONTENT_TYPE_DEFAULT (#460)

Author: dr0i

metafacture-io/src/main/java/org/metafacture/io/HttpOpener.java

@@ -55,6 +55,7 @@ public final class HttpOpener extends DefaultObjectPipe<String, ObjectReceiver<R
 
     private static final String ACCEPT_DEFAULT = "*/*";
     private static final String ACCEPT_HEADER = "accept";
+    private static final String CONTENT_TYPE_DEFAULT = "*/*";
     private static final String CONTENT_TYPE_HEADER = "content-type";
     private static final String DEFAULT_PREFIX = "ERROR: ";
     private static final String ENCODING_DEFAULT = "UTF-8";
@@ -98,7 +99,7 @@ private boolean getInputAsBody() {
      */
     public HttpOpener() {
         setAccept(ACCEPT_DEFAULT);
-        setContentType(ACCEPT_DEFAULT);
+        setContentType(CONTENT_TYPE_DEFAULT);
         setEncoding(ENCODING_DEFAULT);
         setErrorPrefix(DEFAULT_PREFIX);
         setMethod(DEFAULT_METHOD);