install overlaybd snapshotter failed

[zlseu-edu]

Reproduce:

1. just run INSTALL.sh, a shell error occur.

bash INSTALL.sh
Compile overlaybd-snapshotter...
bin/overlaybd-snapshotter
bin/ctr
copy config.json to /etc/overlaybd-snapshotter/
create service...
Would you like make containerd support overlaybd-snapshotter [Y/N]? (this will change /etc/containerd/config.toml and restart containerd) Y
INSTALL.sh: line 41: conditional binary operator expected
INSTALL.sh: line 41: syntax error near `/etc/containerd/config.toml'
INSTALL.sh: line 41: `        if [[ !-f /etc/containerd/config.toml ]]; then'

[liulanzheng]

#93 solved