Update version to v4.0.0

Author: sugyan

linebot/version.go

@@ -11,7 +11,9 @@
 // WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 // License for the specific language governing permissions and limitations
 // under the License.
+//
+// Don't edit this file directly. This file is generated by script/tag.sh .
 
 package linebot
 
-const version = "3.0.0"
+const version = "4.0.0"