Removes --cache from installation instructions

This flag has been deprecated (all queries hit the cache now to protect
users from hitting github rate limits).
Fixes #68

README.md

@@ -59,7 +59,7 @@ Now you can install your [favorite utility](#supported-distributions) just by ty
 ```
 wget -q https://github.com/devops-works/binenv/releases/latest/download/binenv_linux_amd64 -O binenv
 chmod +x binenv
-./binenv update --cache
+./binenv update
 ./binenv install binenv
 rm binenv
 if [[ -n $BASH ]]; then ZESHELL=bash; fi
@@ -75,7 +75,7 @@ exec $SHELL
 ```
 wget -q https://github.com/devops-works/binenv/releases/latest/download/binenv_darwin_amd64 -O binenv
 chmod +x binenv
-./binenv update --cache
+./binenv update
 ./binenv install binenv 
 rm binenv
 echo 'export PATH=~/.binenv:$PATH' >> ~/.bashrc