pixman: Update version from 0.34.0 to 0.38.0

Cairo 1.17.2 requires at least Pixman 0.36.0, so update to the latest
and greatest version [0.38.0][1].

> Changes since 0.36.0:
> - Use floating point calculations for gradients and pixman-bits-image when
>   better accuracy is requested.
> - Add support for the meson build system.

[1]: https://lists.freedesktop.org/archives/pixman/2019-February/004838.html

pixman.be0

@@ -1,6 +1,6 @@
 #!/usr/bin/env beesh
 
-# BEE_VERSION pixman-0.34.0-0
+# BEE_VERSION pixman-0.38.0-0
 
 ## this file was created by bee init and should be executed to build a
 ## bee-package. (Additional hints are located at the end of this file.)