Fix cli help example for specifying several attributes for toxic

[gavvvr]

toxiproxy-cli h t

gives me an incorrect example for adding new toxic:

toxic add: usage: toxiproxy-cli add --type --toxicName \ --attribute --upstream --downstream

example: toxiproxy-cli toxic add myProxy -t latency -n myToxic -a latency=100,jitter=50

This leads to:

Failed to add toxic: AddToxic: HTTP 409: toxic already exists

Correct usage will be (as said in #139):

toxiproxy-cli toxic add myProxy -t latency -n myToxic -a latency=100 -a jitter=50

[miry]

It seems fixed:

$ toxiproxy-cli h t
...
     toxic add:
       usage: toxiproxy-cli toxic add --type <toxicType> [--downstream|--upstream] \
               --toxicName <toxicName> [--toxicity <float>] \
               --attribute <key=value> [--attribute <key2=value2>] <proxyName>

       example: toxiproxy-cli toxic add -t latency -n myToxic -a latency=100 -a jitter=50 myProxy