Update PKGBUILD to current guidelines

PKGBUILD

# Maintainer: Mark Pustjens <pustjens@dds.nl>
# Previous Contributor: Geoffroy Carrier <geoffroy.carrier@koon.fr>
# Previous Contributor: Giorgio Lando <patroclo7@gmail.com>
# Previous Contributor: Leslie P. Polzer <polzer@gnu.org>
pkgname=isync
pkgver=1.1.0
pkgrel=1
pkgdesc="IMAP mail synchronizer for offline/batch mail editing"
url="http://isync.sourceforge.net/"
arch=(i686 x86_64)
license=(GPL)
depends=(openssl)
source=(http://downloads.sourceforge.net/sourceforge/isync/$pkgname-$pkgver.tar.gz)
sha256sums=('51f5618c239013fb770f98ae269f24ee417214efaaf7e22821b4a27cf9a9213c')

build() {
  cd "${srcdir}"/$pkgname-$pkgver
  ./configure --prefix=/usr
  make
}

package() {
  cd "${srcdir}"/$pkgname-$pkgver
  make DESTDIR="$pkgdir" install
}