add try-mathbox psc-package (package set psc-0.11.6) (#105)

Author: rintcius

staging/mathbox/psc-package.json

@@ -0,0 +1,8 @@
+{
+    "name": "trymathbox",
+    "set": "psc-0.11.6",
+    "source": "https://github.com/purescript/package-sets.git",
+    "depends": [
+        "mathbox"
+    ]
+}