Remove bash in install script to support alpine (#4)

scripts/install_plugin.sh

@@ -1,10 +1,7 @@
-#!/bin/bash -e
+#!/bin/sh -e
 
 # Copied w/ love from the excellent hypnoglow/helm-s3
 
-DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
-cd $DIR/../
-
 if [ -n "${HELM_PUSH_PLUGIN_NO_INSTALL_HOOK}" ]; then
     echo "Development mode: not downloading versioned release."
     exit 0