[flowplayer.spec] Add missing BuildRequires: pkgconfig(Qt5Xml) (#39)

Fixes issue #38

rpm/flowplayer.spec

@@ -21,7 +21,7 @@ Version:    0.3.1
 # build at GitHub and OBS, when configured accordingly; mind the sorting
 # (`adud` < `alpha`).  For details and reasons, see
 # https://github.com/storeman-developers/harbour-storeman/wiki/Git-tag-format
-Release:    rc2
+Release:    rc3
 # The Group tag should comprise one of the groups listed here:
 # https://github.com/mer-tools/spectacle/blob/master/data/GROUPS
 Group:      Applications/Multimedia
@@ -45,6 +45,7 @@ Requires:   qml(org.nemomobile.thumbnailer)
 Requires:   qml(com.jolla.mediaplayer)
 BuildRequires:  pkgconfig(sailfishapp) >= 1.0.2
 BuildRequires:  pkgconfig(Qt5Core)
+BuildRequires:  pkgconfig(Qt5Xml)
 BuildRequires:  pkgconfig(Qt5Qml)
 BuildRequires:  pkgconfig(Qt5Quick)
 BuildRequires:  pkgconfig(gstreamer-1.0)