Check for changes to the Gem dependencies only when running in our co…

…… (#265)

docker/build/run.sh

@@ -1,13 +1,15 @@
 #!/bin/bash
 
-sha256sum --check /build.sha256 >/dev/null 2>&1
-if [[ $? -ne 0 ]]; then
-  echo "#####################################################################"
-  echo "#  WARNING! Gemfile dependencies have changed from this container.  #"
-  echo "#  Rebuild this container to ensure you are running with the latest #"
-  echo "#  dependencies.                                                    #"
-  echo "#####################################################################"
-  exit 1
+if [[ -f /build.sha256 ]]; then
+    sha256sum --check /build.sha256 >/dev/null 2>&1
+    if [[ $? -ne 0 ]]; then
+        echo "#####################################################################"
+        echo "#  WARNING! Gemfile dependencies have changed from this container.  #"
+        echo "#  Rebuild this container to ensure you are running with the latest #"
+        echo "#  dependencies.                                                    #"
+        echo "#####################################################################"
+        exit 1
+    fi
 fi
 
 case "${1}" in