Revert "Use cd instead of WORKDIR in Dockerfile"

Author: murgatroid99

packages/grpc-js-xds/interop/Dockerfile

@@ -22,8 +22,10 @@ FROM node:16-alpine as build
 WORKDIR /node/src/grpc-node
 COPY . .
 
-RUN cd packages/grpc-js && npm install
-RUN cd packages/grpc-js-xds && npm install
+WORKDIR /node/src/grpc-node/packages/grpc-js
+RUN npm install
+WORKDIR /node/src/grpc-node/packages/grpc-js-xds
+RUN npm install
 
 FROM node:16-alpine
 WORKDIR /node/src/grpc-node