ClassNotFoundException: clojure.lang.AFunction

This is weird. Few days ago it was working fine, now out of a sudden not anymore. Any boot commands, even invalid ones, do nothing.

`boot sdfsdfsdfs` just returns an empty line.

but `boot --version` works fine:

```
└─❱❱❱ boot --version
#http://boot-clj.com
#Wed Aug 23 10:06:42 NZST 2017
BOOT_CLOJURE_NAME=org.clojure/clojure
BOOT_CLOJURE_VERSION=1.8.0
BOOT_VERSION=2.6.0
```

and when I run in verbose mode, there is some output but at the end it just does nothing:

```
└─❱❱❱ boot -v +4839 10:09 ❰─┘
Acquired java.util.concurrent.Semaphore@6754ef00[Permits = 0]...
Syncing project dirs to temp dirs...
Filesystem: copying (removed)
Sync complete.
Released java.util.concurrent.Semaphore@6754ef00[Permits = 1]...
Acquired java.util.concurrent.Semaphore@6754ef00[Permits = 0]...
Syncing project dirs to temp dirs...
Filesystem: copying index.html...
Sync complete.
Released java.util.concurrent.Semaphore@6754ef00[Permits = 1]...
```

I am on latest Mac OS here

Start by reproducing `boot sdfsdfsdfs` and `boot -v` on the reported Mac OS setup, then compare the silent behavior with the reported `ClassNotFoundException: clojure.lang.AFunction`. Done means identifying a reproducible cause and confirming that valid and invalid Boot commands produce their expected output.

Written by the indexing model from the issue text.