Apply #289 revert to new Buster variants too

Author: tianon

2.5/buster/Dockerfile

@@ -83,7 +83,7 @@ RUN set -eux; \
 # install things globally, for great justice
 # and don't create ".bundle" in all our apps
 ENV GEM_HOME /usr/local/bundle
-ENV BUNDLE_PATH__SYSTEM=true \
+ENV BUNDLE_PATH="$GEM_HOME" \
 	BUNDLE_SILENCE_ROOT_WARNING=1 \
 	BUNDLE_APP_CONFIG="$GEM_HOME"
 # path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438

2.5/buster/slim/Dockerfile

@@ -109,7 +109,7 @@ RUN set -eux; \
 # install things globally, for great justice
 # and don't create ".bundle" in all our apps
 ENV GEM_HOME /usr/local/bundle
-ENV BUNDLE_PATH__SYSTEM=true \
+ENV BUNDLE_PATH="$GEM_HOME" \
 	BUNDLE_SILENCE_ROOT_WARNING=1 \
 	BUNDLE_APP_CONFIG="$GEM_HOME"
 # path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438

2.6/buster/Dockerfile

@@ -79,7 +79,7 @@ RUN set -eux; \
 # install things globally, for great justice
 # and don't create ".bundle" in all our apps
 ENV GEM_HOME /usr/local/bundle
-ENV BUNDLE_PATH__SYSTEM=true \
+ENV BUNDLE_PATH="$GEM_HOME" \
 	BUNDLE_SILENCE_ROOT_WARNING=1 \
 	BUNDLE_APP_CONFIG="$GEM_HOME"
 # path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438

2.6/buster/slim/Dockerfile

@@ -105,7 +105,7 @@ RUN set -eux; \
 # install things globally, for great justice
 # and don't create ".bundle" in all our apps
 ENV GEM_HOME /usr/local/bundle
-ENV BUNDLE_PATH__SYSTEM=true \
+ENV BUNDLE_PATH="$GEM_HOME" \
 	BUNDLE_SILENCE_ROOT_WARNING=1 \
 	BUNDLE_APP_CONFIG="$GEM_HOME"
 # path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438