update vault to use 1.15.4 release (#16)

Signed-off-by: cpanato <ctadeu@gmail.com>

README.md

@@ -11,7 +11,7 @@ Add the following entry to your Github workflow YAML file:
 ```yaml
 uses: cpanato/vault-installer@main
 with:
-  vault-release: '1.12.1' # optional
+  vault-release: '1.15.4' # optional
 ```
 
 Example using a pinned version:
@@ -28,7 +28,7 @@ jobs:
       - name: Install Vault
         uses: cpanato/vault-installer@main
         with:
-          vault-release: '1.12.1'
+          vault-release: '1.15.4'
       - name: Check install!
         run: vault version
 ```

action.yml

@@ -10,7 +10,7 @@ inputs:
   vault-release:
     description: 'Hashicorp Vault release version to be installed'
     required: false
-    default: '1.12.2'
+    default: '1.15.4'
   install-dir:
     description: 'Where to install the Hashicorp Vault binary'
     required: false
@@ -145,7 +145,7 @@ runs:
           log_info "Im running here without windows '${{ runner.os }}'"
           shaprog ${desired_vault_filename} SHA256SUMS
         fi
-      
+
         ret=$?
         if [[ $retVal -eq 0 ]]; then
           log_info "unpacking!"