ruby-xapian-full: corrected installation path

pkgbuild/ruby-xapian-full/PKGBUILD

@@ -2,7 +2,7 @@
 # Contributor: David Campbell <davekong@archlinux.us>
 pkgname=ruby-xapian-full
 pkgver=1.2.3
-pkgrel=3
+pkgrel=4
 pkgdesc="Xapian bindings for Ruby without dependency on system Xapian library"
 arch=('i686' 'x86_64')
 url="http://rubygems.org/gems/xapian-full"
@@ -19,7 +19,6 @@ options=('!makeflags' '!libtool')
 
 build() {
   cd "$srcdir"
-  local _gemdir="$(ruby -rubygems -e'puts Gem.default_dir')"
 
   #patch Rakefile
   echo "Patching Rakefile ..."
@@ -38,6 +37,7 @@ build() {
 
 package(){
   cd "$srcdir"
+  local _gemdir="$(ruby -rubygems -e'puts Gem.default_dir')"
   echo "Installing gem..."
   gem install --no-user-install --ignore-dependencies --verbose -i "$pkgdir$_gemdir" -n "$pkgdir"/usr/bin xapian-full-$pkgver.gem 
 }