Simplify regex matching in build-deb.sh.

remoting/host/installer/linux/build-deb.sh

 #!/bin/bash -e
 
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 if [[ -z "$version_full" ]]; then
   src_root=./../../../..
   version_helper=$src_root/chrome/tools/build/version.py
   version_base=$($version_helper -f $src_root/remoting/VERSION \
                  -t "@MAJOR@.@MINOR@")
   version_build=$($version_helper -f $src_root/chrome/VERSION \
                   -t "@BUILD@.@PATCH@")
   version_full="$version_base.$version_build"
 fi
 
-if !(echo $version_full | grep -E \
-     "^[[:digit:]]+.[[:digit:]]+.[[:digit:]]+.[[:digit:]]+$" > /dev/null); then
+if [[ ! "$version_full" =~ ^[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+$ ]]; then
   echo "Error: Invalid \$version_full value: $version_full" >&2
   exit 1
 fi
 
 echo "Building version $version_full"
 
 # Create a fresh debian/changelog.
 export DEBEMAIL="The Chromium Authors <chromium-dev@chromium.org>"
 rm -f debian/changelog
 debchange --create \
   --package chrome-remote-desktop \
   --distribution lucid \
   --newversion "$version_full" \
   "New Debian package"
 
 dpkg-buildpackage -b -us -uc