lg-hammerhead: bump pkgrel (!1079)

The pkgrel bump in !1032 got lost during a rebase, rebuild the package to fix:
ERROR: Could not find dependency 'modem-qcom-msm-mainline-common' in any aports folder or APKINDEX.

device/testing/device-lg-hammerhead/APKBUILD

@@ -2,7 +2,7 @@
 # Contributor: Martijn Braam <martijn@brixit.nl>
 pkgname=device-lg-hammerhead
 pkgver=2
-pkgrel=17
+pkgrel=18
 pkgdesc="Google Nexus 5"
 url="https://postmarketos.org"
 arch="armv7"