Dockerfile: fix mixed indentation (#2727)

.editorconfig

@@ -7,6 +7,10 @@ insert_final_newline = true
 indent_style = tab
 charset = utf-8
 
+[Dockerfile]
+indent_style = space
+indent_size = 4
+
 [/patches/**]
 indent_style = unset
 indent_size = unset

contrib/docker/Dockerfile

@@ -21,8 +21,8 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     ecdsautils \
     lua-check \
     shellcheck \
-  && apt-get clean \
-  && rm -rf /var/lib/apt/lists/*
+    && apt-get clean \
+    && rm -rf /var/lib/apt/lists/*
 
 RUN useradd -d /gluon gluon
 USER gluon