Setup GOROOT on init.

Try to add a start of answer to #21.

I am not a bash guy, so this may not be idiomatic.

Author: yageek

libexec/goenv-init

@@ -87,10 +87,12 @@ mkdir -p "${GOENV_ROOT}/"{shims,versions}
 case "$shell" in
 fish )
   echo "setenv PATH '${GOENV_ROOT}/shims' \$PATH"
+  echo "setenv GOROOT '$(goenv prefix)'"
   echo "setenv GOENV_SHELL $shell"
 ;;
 * )
   echo 'export PATH="'${GOENV_ROOT}'/shims:${PATH}"'
+  echo 'export GOROOT="$(goenv prefix)"'
   echo "export GOENV_SHELL=$shell"
 ;;
 esac