fixed build broken under freebsd

Author: francoiscolas

binding.gyp

@@ -18,6 +18,10 @@
           'include_dirs': ['<!@(pg_config --includedir)'],
           'libraries' : ['-lpq -L<!@(pg_config --libdir)']
         }],
+        ['OS=="freebsd"', {
+          'include_dirs': ['<!@(pg_config --includedir)'],
+          'libraries' : ['-lpq -L<!@(pg_config --libdir)']
+        }],
         ['OS=="win"', {
           'include_dirs': ['<!@(pg_config --includedir)'],
           'libraries' : ['libpq.lib'],