Change license value

Packagistで以下エラーが発生したため
Importing branch master (dev-master)
Skipped branch master, Invalid package information:
License "NetCommons License" is not a valid SPDX license identifier, see
https://spdx.org/licenses/ if you use an open license.
If the software is closed-source, you may use "proprietary" as license.

Conflicts:
	composer.json

composer.json

@@ -11,7 +11,8 @@
         "cakedc/migrations":            "~2.2",
         "netcommons/net-commons":       "dev-master"
     },
-    "license": "NetCommons License",
+    "license": "LicenseRef-NetCommons",
+    "license-ref-net-commons": "https://raw.githubusercontent.com/NetCommons3/NetCommons3/master/license.txt",
     "authors": [
         {
           "name": "Ryuji AMANO (RYUS INC.)",