Add missing Shader:getVariable argument description;

api/init.lua

@@ -22833,7 +22833,8 @@ return {
                   arguments = {
                     {
                       name = "name",
-                      type = "string"
+                      type = "string",
+                      description = "The name of the variable to check."
                     }
                   },
                   returns = {

api/lovr/graphics/Shader/hasVariable.lua

@@ -4,6 +4,7 @@ return {
   arguments = {
     name = {
       type = 'string',
+      description = 'The name of the variable to check.'
     }
   },
   returns = {