Make version.sh use VERSION file

Hardcoding the version means it will often be out of date.

README.md

@@ -177,10 +177,10 @@ Currently, the `@compat` macro supports the following syntaxes:
 If you're adding additional compatibility code to this package, the [`bin/version.sh` script is useful for extracting the version number from a git commit SHA. For example, from the git repository of `julia`, run something like this:
 
 ```sh
-bash $ /path/to/Compat/bin/version.sh e3aa57efbc6542efbcc7feac9b1309d628ac6f12
-2418
+bash $ /path/to/Compat/bin/version.sh a378b60fe483130d0d30206deb8ba662e93944da
+0.5.0-dev+2023
 ```
 
 This prints a number `XXXX`, and you can then test whether Julia
-is at least this version by `VERSION >= v"0.4.0-dev+XXXX"` (assuming
-it is a commit from the 0.4 development cycle).
+is at least this version by `VERSION >= v"0.Y.0-dev+XXXX"` (assuming
+it is a commit from the 0.Y development cycle).

bin/version.sh

@@ -1,4 +1,5 @@
 #!/bin/bash
 last_tag=$(git describe --tags --abbrev=0)
-echo -n "0.4.0-dev+"
-git rev-list $1 ^$last_tag | wc -l | sed -e 's/[^[:digit:]]//g'
+ver=$(cat VERSION)
+nb=$(git rev-list $1 ^$last_tag | wc -l | sed -e 's/[^[:digit:]]//g')
+echo "$ver+$nb"