fix(docker):avoid error in some cases by creating fake duniter-cucumber

docker/Dockerfile

@@ -27,6 +27,14 @@ RUN test -x build/duniter || \
         mv target/release/duniter build/ \
     )
 
+# Create fake duniter-cucumber if is not exist
+# The goal is to avoid error later, this binary is optional
+RUN test -x build/duniter-cucumber || \
+    ( \
+        mkdir -p build && \
+        touch build/duniter-cucumber \
+    )
+
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 # Final Stage
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