Patch docker conda install pip requirements (#1094)

Install getting stuck on user prompt:

sd  | Obtaining GFPGAN from git+https://github.com/TencentARC/GFPGAN#egg=GFPGAN (from -r /sd/condaenv.h7qk_3wn.requirements.txt (line 25))
sd  | What to do?  (i)gnore, (w)ipe, (b)ackup 
sd  | failed
sd  | 
sd  | CondaEnvException: Pip failed

this defaults the pip exists action to wiping the already existing lib and re-downloading it

docker-compose.yml

@@ -7,6 +7,8 @@ services:
       context: .
       dockerfile: Dockerfile
     env_file: .env_docker
+    environment:
+      PIP_EXISTS_ACTION: w
     volumes:
       - .:/sd
       - ./outputs:/sd/outputs