libpng version was outdated and could not be downloaded anymore. Updated

to 1.2.42.
Signed-off-by: Jan Roesner <jan@roesner.it>

magick-installer.sh

@@ -12,7 +12,7 @@ function download() {
 }
 
 download http://nongnu.askapache.com/freetype/freetype-2.4.3.tar.gz
-download http://surfnet.dl.sourceforge.net/project/libpng/libpng-stable/1.2.39/libpng-1.2.39.tar.gz
+download http://surfnet.dl.sourceforge.net/project/libpng/libpng-stable/1.2.42/libpng-1.2.42.tar.gz
 download http://www.ijg.org/files/jpegsrc.v8b.tar.gz
 download http://www.sfr-fresh.com/unix/misc/tiff-3.9.4.tar.gz
 download http://voxel.dl.sourceforge.net/project/wvware/libwmf/0.2.8.4/libwmf-0.2.8.4.tar.gz
@@ -29,8 +29,8 @@ make
 sudo make install
 cd ..
 
-tar xzvf libpng-1.2.39.tar.gz
-cd libpng-1.2.39
+tar xzvf libpng-1.2.42.tar.gz
+cd libpng-1.2.42
 ./configure --prefix=/usr/local
 make clean
 make