update graphics/sketch

The 0.3.7 version has been released in 2012, it's time to update the
port... The version seems to be code cleanup and adding asin and acos
function.

Examples provided seems to work.

Index: Makefile
===================================================================
RCS file: /cvs/ports/graphics/sketch/Makefile,v
retrieving revision 1.2
diff -u -p -r1.2 Makefile
--- Makefile 11 Mar 2013 11:10:55 -0000 1.2
+++ Makefile 10 Aug 2018 22:26:03 -0000
@@ -2,7 +2,7 @@

COMMENT = 3D scene description translator for TeX

-DISTNAME = sketch-0.3.2
+DISTNAME = sketch-0.3.7
EXTRACT_SUFX = .tgz

CATEGORIES = graphics
Index: distinfo
===================================================================
RCS file: /cvs/ports/graphics/sketch/distinfo,v
retrieving revision 1.2
diff -u -p -r1.2 distinfo
--- distinfo 18 Jan 2015 03:14:14 -0000 1.2
+++ distinfo 10 Aug 2018 22:26:03 -0000
@@ -1,2 +1,2 @@
-SHA256 (sketch-0.3.2.tgz) = 9vyJH881KEwBiqZ4a69nQpSU90mcUzt5AbDnQbKo5S8=
-SIZE (sketch-0.3.2.tgz) = 2881333
+SHA256 (sketch-0.3.7.tgz) = EpYq1f5aD3yfxthL1NCbh5u/YEl1yDlAXxYTvmV7qAQ=
+SIZE (sketch-0.3.7.tgz) = 2882384