docker: Switch stable version to v0.2.0

This switches the stable version of the dcrror Dockerfile to use the
recently tagged v0.2.0 version, which embeds the v1.7.5 release of the
Decred tools.

Dockerfile

@@ -11,13 +11,13 @@ FROM golang:1.17-buster AS builder
 
 # Build dcrd and include dcrctl as well.
 RUN git clone https://github.com/decred/dcrd
-RUN (cd dcrd && git checkout release-v1.6.2)
+RUN (cd dcrd && git checkout release-v1.7.5)
 RUN (cd dcrd && go install .)
 RUN git clone https://github.com/decred/dcrctl
-RUN (cd dcrctl && git checkout release-v1.6.2)
+RUN (cd dcrctl && git checkout release-v1.7.5)
 RUN (cd dcrctl && go install .)
 RUN git clone https://github.com/decred/dcrros
-RUN (cd dcrros && git checkout release-v0.1.1)
+RUN (cd dcrros && git checkout release-v0.2.0)
 RUN (cd dcrros && go install .)
 
 # Stage 2: Build the final image starting from a cleaner base.