libgd requires libpng and `cd src`

packages/libgd.rb

@@ -5,6 +5,8 @@ class Libgd < Package
   source_url 'https://github.com/libgd/libgd/archive/GD_2_0_33.tar.gz'
   source_sha1 '489e25f18d3fc9d7f8b0e4889f98f5aa25363c3e'
 
+  depends_on 'libpng'
+
   def self.build
     FileUtils.cd('src') do
       system "./configure --libdir=/usr/local/lib#{SHORTARCH}/ CC=\"gcc -m#{SHORTARCH}\" CFLAGS=\" -fPIC\""
@@ -13,6 +15,8 @@ class Libgd < Package
   end
 
   def self.install
+    FileUtils.cd('src') do
       system "make", "DESTDIR=#{CREW_DEST_DIR}", "install"
     end
+  end
 end