pixman: Update version from 0.38.0 to 0.38.4

From the [0.38.2 announcement][1]:

> Log:
> 	Dylan Baker (6):
> 	      meson: work around meson issue #5115
> 	      meson: fix typo which breaks loongson checks
> 	      meson: fix copy-n-paste error for arm simd assembly
> 	      meson: Add proper include paths for the loongson check
> 	      meson: simplify and fix mmx library compilation
> 	      meson: store ARM SIMD and NEON tests as text files
>
> 	Matt Turner (2):
> 	      meson: Correct copy-and-paste mistake
> 	      Pre-release version bump to 0.38.2
>
> 	Niveditha Rau (1):
> 	      void function should not return a value
>
> 	Simon Richter (2):
> 	      Windows: Show compiler invocation
> 	      Windows: Support building with SHELL=cmd.exe
>

From the [0.38.4 announcement][2]:

> Log:
> 	Matt Turner (4):
> 	      Post-release version bump to 0.38.3
> 	      Makefile.am: Update download links
> 	      Makefile.am: Ship Meson assembly test files in the tarball
> 	      Pre-release version bump to 0.38.4

[1]: https://lists.x.org/archives/xorg-announce/2019-April/002990.html
[2]: https://lists.x.org/archives/xorg-announce/2019-April/002991.html

pixman.be0

@@ -1,6 +1,6 @@
 #!/usr/bin/env beesh
 
-# BEE_VERSION pixman-0.38.0-0
+# BEE_VERSION pixman-0.38.4-0
 
 ## 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.)