PackageToJS: Inherit swift package -c configuration by default

#309 introduced `-c`
option to the plugin side in addition to the `swift package`'s one.
However `swift package -c release js` was building with release config
before 0.25.0 but it started to build with debug config as the default
in 0.25.0. This change makes the plugin to respect the `swift package`'s
one if `-c` is not specified after `js` plugin name

Author: kateinoigakukun

Plugins/PackageToJS/Sources/PackageToJSPlugin.swift

@@ -323,7 +323,7 @@ struct PackageToJSPlugin: CommandPlugin {
             }
             buildConfiguration = _buildConfiguration
         } else {
-            buildConfiguration = .debug
+            buildConfiguration = .inherit
         }
         var parameters = PackageManager.BuildParameters(
             configuration: buildConfiguration,