user/cairomm: make virtual dependency explicit. fixes #1150.

user/cairomm/APKBUILD

@@ -10,13 +10,13 @@ options="!check" # broken test
 license="LGPL-2.1+"
 depends=""
 makedepends="boost-dev cairo-dev doxygen fontconfig-dev glibmm-dev graphviz
-	libsigc++-dev meson ninja cmd:xsltproc"
+	libsigc++-dev meson ninja libxslt"
 subpackages="$pkgname-dev $pkgname-doc"
 source="https://www.cairographics.org/releases/cairomm-$pkgver.tar.xz"
 
 build() {
 	meson \
-	    	--prefix=/usr \
+		--prefix=/usr \
 		--sysconfdir=/etc \
 		--mandir=/usr/share/man \
 		--localstatedir=/var \