Update composer.json

switching to PSR-4 autoloading standard

composer.json

@@ -1,7 +1,7 @@
 {
     "name": "robthree/twofactorauth",
     "description": "Two Factor Authentication",
-    "version": "1.5.1",
+    "version": "1.5.2",
     "type": "library",
     "keywords": [ "Authentication", "Two Factor Authentication", "Multi Factor Authentication", "TFA", "MFA", "PHP", "Authenticator", "Authy" ],
     "homepage": "https://github.com/RobThree/TwoFactorAuth",
@@ -17,12 +17,20 @@
         "issues": "https://github.com/RobThree/TwoFactorAuth/issues",
         "source": "https://github.com/RobThree/TwoFactorAuth"
     },
-    "autoload": {
-        "classmap": [
-            "lib/"
-        ]
-    },
     "require": {
         "php": ">=5.3.0"
+    },
+    "require-dev": {
+        "phpunit/phpunit": "@stable"
+    },
+    "autoload": {
+        "psr-4": {
+            "RobThree\\Auth\\": "lib"
+        }
+    },
+    "autoload-dev": {
+        "psr-4": {
+            "RobThree\\Auth\\Test\\": "tests"
+        }
     }
 }