Fixed 2.12.0 download url (#14)

Author: oconnormi

2.12.0/linux/alpine/Dockerfile

@@ -2,7 +2,7 @@ FROM alpine
 ENV DDF_VERSION=2.12.0
 RUN apk add --no-cache curl unzip
 RUN curl -o ddf.zip \
-  "http://artifacts.codice.org/service/local/artifact/maven/content?g=org.codice.ddf&a=ddf&v=$DDF_VERSION&r=RELEASES&e=zip"
+  "http://artifacts.codice.org/service/local/artifact/maven/content?g=org.codice.ddf&a=ddf&v=$DDF_VERSION&r=releases&e=zip"
 RUN unzip ddf.zip
 RUN mv ddf-${DDF_VERSION} /ddf