Bump version to 0.3.1

This change bumps the version of the crate to 0.3.1. The following
notable changes have been made since 0.3.0:
- Introduced lock file usage to prevent multiple program instances from
  running concurrently
  - Added --force/-f option to force starting up in the presence of
    a stale lock file
- Made sure to write-protect config files and tasks while the program is
  running, to prevent accidental overwriting of intentional changes
- Properly support scrolling when editing tasks not fitting on the
  screen
- Set positive tag literals of tab as tags on a task newly added to an
  empty tab
- Removed support for writing output to a file provided as program
  argument
- Added support for --version/-V option to print program version
- Bumped termion dependency to 2.0

CHANGELOG.md

@@ -1,5 +1,5 @@
-Unreleased
-----------
+0.3.1
+-----
 - Introduced lock file usage to prevent multiple program instances from
   running concurrently
   - Added `--force`/`-f` option to force starting up in the presence of

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "notnow"
-version = "0.3.0"
+version = "0.3.1"
 edition = "2021"
 rust-version = "1.65"
 authors = ["Daniel Mueller <deso@posteo.net>"]
@@ -25,7 +25,7 @@ keywords = [
 description = """
 A terminal based task and TODO management software.
 """
-include = ["src/**/*", "LICENSE", "README.md", "CHANGELOG.md"]
+include = ["build.rs", "src/**/*", "LICENSE", "README.md", "CHANGELOG.md"]
 
 [profile.release]
 opt-level = "z"