pycairo: set user-agent to fix download of patches

pkgs/development/python-modules/pycairo/default.nix

···
 
   patches = [(fetchpatch {
     url = http://www.linuxfromscratch.org/patches/blfs/svn/pycairo-1.10.0-waf_unpack-1.patch;
+    curlOpts = "--user-agent 'Mozilla/5.0'";
     sha256 = "1bmrhq2nmhx4l5glvyi59r0hc7w5m56kz41frx7v3dcp8f91p7xd";
   })];
 
   patch_waf = fetchpatch {
     url = http://www.linuxfromscratch.org/patches/blfs/svn/pycairo-1.10.0-waf_python_3_4-1.patch;
+    curlOpts = "--user-agent 'Mozilla/5.0'";
     sha256 = "0xfl1i9dips2nykyg91f5h5r3xpk2hp1js1gq5z0hwjr0in55id4";
   };