Improve version extraction regex in pkgver

.SRCINFO

@@ -1,6 +1,6 @@
 pkgbase = lv2-git
 	pkgdesc = Plugin standard for audio systems (git version)
-	pkgver = 1.18.7.r1399.8124b4e
+	pkgver = 1.18.8.r1419.bd69ed7
 	pkgrel = 1
 	url = http://lv2plug.in/
 	arch = i686
@@ -29,7 +29,7 @@ pkgbase = lv2-git
 	optdepends = python-pygments: for lv2specgen.py
 	optdepends = python-rdflib: for lv2specgen.py
 	provides = lv2
-	provides = lv2=1.18.7
+	provides = lv2=1.18.8
 	conflicts = lv2
 	source = lv2::git+https://gitlab.com/lv2/lv2.git
 	sha256sums = SKIP

PKGBUILD

@@ -2,8 +2,8 @@
 # Contributor: speps <speps at aur dot archlinux dot org>
 
 _pkgname=lv2
-pkgname="$_pkgname-git"
-pkgver=1.18.7.r1399.8124b4e
+pkgname=$_pkgname-git
+pkgver=1.18.8.r1419.bd69ed7
 pkgrel=1
 pkgdesc='Plugin standard for audio systems (git version)'
 arch=(i686 x86_64)
@@ -43,7 +43,7 @@ sha256sums=('SKIP')
 
 pkgver() {
   cd $_pkgname
-  local ver=$(grep -E "^\s+version: '.*'" meson.build | cut -d "'" -f 2)
+  local ver=$(grep -E "^\s+version: '[0-9]+\.[0-9]+\.[0-9]+'" meson.build | cut -d "'" -f 2)
   echo ${ver}.r$(git rev-list --count HEAD).$(git rev-parse --short HEAD)
 }