DiffFileInfo: Export it back again

It should be still exported as it's a part of
FileData class, which is also exported.

Amends b677fbe992

Change-Id: I0d53dff2c355cddf7d1f3d001cb7b71210c75223
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/diffeditor/diffutils.h

@@ -21,7 +21,7 @@ namespace Utils { class Diff; }
 
 namespace DiffEditor {
 
-class DiffFileInfo {
+class DIFFEDITOR_EXPORT DiffFileInfo {
 public:
     enum PatchBehaviour {
         PatchFile,