Fixes docker image location paths

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previous paths for FROM statements did not resolve correctly. They threw this error:

Building web
[+] Building 2.9s (4/4) FINISHED
 => [internal] load build definition from Dockerfile                                                                                                                                              0.0s
 => => transferring dockerfile: 749B                                                                                                                                                              0.0s 
 => [internal] load .dockerignore                                                                                                                                                                 0.0s 
 => => transferring context: 35B                                                                                                                                                                  0.0s 
 => CANCELED [internal] load metadata for docker.io/dotnet/sdk:2.0                                                                                                                                2.8s 
 => ERROR [internal] load metadata for docker.io/dotnet/aspnet:2.0                                                                                                                                1.9s
------
 > [internal] load metadata for docker.io/dotnet/aspnet:2.0:
------
failed to solve with frontend dockerfile.v0: failed to create LLB definition: pull access denied, repository does not exist or may require authorization: server message: insufficient_scope: authorization failed
ERROR: Service 'web' failed to build : Build failed