netpbm: Update and remove invalid "r" prefix

Otherwise dpkg fails with "version number does not start with digit".

Fixes #18.

packages/netpbm/build.sh

@@ -4,8 +4,8 @@ TERMUX_PKG_DESCRIPTION="Toolkit for manipulation of graphic images, including co
 # and are divided among (1) Development, (2) Advanced, (3) Stable and (4) Super Stable.
 # Only Super Stable is distributed as a tar ball, but is outdated and does not compile with modern libpng.
 # So use revisions from http://svn.code.sf.net/p/netpbm/code/advanced for packages.
-_SVN_REVISION=2592
-TERMUX_PKG_VERSION=r${_SVN_REVISION}
+_SVN_REVISION=2643
+TERMUX_PKG_VERSION=${_SVN_REVISION}
 TERMUX_PKG_DEPENDS="libpng, libxml2"
 TERMUX_PKG_BUILD_IN_SRC=yes
 TERMUX_MAKE_PROCESSES=1