fix unicode issue #3753

fixes the unicode issue #3753

I don't know much CPP and Qt but after some google research I found this http://wiki.qt.io/Strings_and_encodings_in_Qt
it does mention trUtf8() that has done the trick for me on Linux with Gnome 3.16.
Haven't tested it on other systems

src/gui/folderstatusmodel.cpp

@@ -791,7 +791,7 @@ void FolderStatusModel::slotSetProgress(const ProgressInfo &progress)
 #ifdef Q_OS_WIN
                 fileProgressString.append(tr("download %1/s").arg(Utility::octetsToString(estimatedDownBw)));
 #else
-                fileProgressString.append(tr("\u2193" " %1/s").arg(Utility::octetsToString(estimatedDownBw)));
+                fileProgressString.append(trUtf8("\u2193" " %1/s").arg(Utility::octetsToString(estimatedDownBw)));
 #endif
             }
             if (estimatedUpBw > 0) {
@@ -799,7 +799,7 @@ void FolderStatusModel::slotSetProgress(const ProgressInfo &progress)
  #ifdef Q_OS_WIN
                 fileProgressString.append(tr("upload %1/s").arg(Utility::octetsToString(estimatedUpBw)));
 #else
-                fileProgressString.append(tr("\u2191" " %1/s").arg(Utility::octetsToString(estimatedUpBw)));
+                fileProgressString.append(trUtf8("\u2191" " %1/s").arg(Utility::octetsToString(estimatedUpBw)));
 #endif
             }
         } else {