appveyor: remove shallow_clone
appveyor: remove shallow_clone

MathieuCassagne/leveldown,Level/rocksdb,Level/leveldown,MathieuCassagne/leveldown,ralphtheninja/leveldown,Level/leveldown,MathieuCassagne/leveldown,MathieuCassagne/leveldown,ralphtheninja/leveldown,ralphtheninja/leveldown,ralphtheninja/leveldown,Level/rocksdb,MathieuCassagne/leveldown,Level/leveldown,ralphtheninja/leveldown,Level/rocksdb