[BUG FIX]: invalid meson version detection

Hi.

I looked at meson.build file at found an incorrectly used function to

determine postgres version.

> if pg_version.endswith('devel')
>   pg_version_arr = [pg_version.split('devel')[0], '0']

There should be `pg_version.contains('devel')`, not `endswith`. Like this:

-if pg_version.endswith('devel')
+if pg_version.contains('devel')

Next statement seems to be valid:

>elif pg_version.contains('beta')
>  pg_version_arr = [pg_version.split('beta')[0], '0']
>elif pg_version.contains('rc')
>  pg_version_arr = [pg_version.split('rc')[0], '0']
>else
>  pg_version_arr = pg_version.split('.')
>endif

I created a single line patch for it.