Fix support of anonymous functions

[viesti]

Since

user=> (pk/mount! #(println “hello”) “/anon”)
Zip size 5.6MB

AWSLambdaException 1 validation error detected: Value null at ‘functionName’ failed to satisfy constraint: Member must not be null (Service: AWSLambda; Status Code: 400; Error Code: ValidationException; Request ID: 235ce99f-9167-11e7-af7c-e74e290cd085)  com.amazonaws.http.AmazonHttpClient$RequestExecutor.handleErrorResponse (AmazonHttpClient.java:1587)

the class name would serve us here.