Increase Julia compat version to 1.4

While I would like to support older versions of Julia, currently this
will be a little bit of work that I don't want to have to do at the
current point in time.  Increasing Julia compat version to version 1.4
in the interest of `readdir`'s keyword arguments `join` and `sort`,
the former of which is used in src/Utils.jl methods for training a
Voila Jones model.  It wouldn't be hard to implement `join` manually,
but I know not what else will need fixing in older versions of Julia,
and I don't even know if people use this package, let alone use this
package with Julia version < 1.4.  Perhaps upon request I will support
Julia versions < 1.4, but for now, this compat version will do.

.github/workflows/CI.yml

@@ -15,8 +15,8 @@ jobs:
       fail-fast: false
       matrix:
         version:
-          - "1.3"
-          - "1.6"
+          - "1.4"       # Old version: requires 1.4 for kwargs in readdir
+          - "1.6"       # Current LTS
           - "nightly"   # Latest Release
         os:
           - ubuntu-latest

Project.toml

@@ -28,7 +28,7 @@ IntegralArrays = "0.1"
 Netpbm = "1"
 ProgressMeter = "1"
 QuartzImageIO = "0.7"
-julia = "1"
+julia = "1.4"
 
 [extras]
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"