Update phpmath

Release 0.3.0 has a security fix in it...

PHPOffice/Math@0.2.0...master

Author: eileenmcnaughton

composer.json

@@ -112,7 +112,7 @@
         "ext-zip": "*",
         "ext-json": "*",
         "ext-xml": "*",
-        "phpoffice/math": "^0.2"
+        "phpoffice/math": "^0.3"
     },
     "require-dev": {
         "ext-libxml": "*",