docker: Use alpine 3.12 temporarily

Author: frangarcj

Dockerfile

@@ -1,5 +1,5 @@
 # First stage of Dockerfile
-FROM alpine:latest
+FROM alpine:3.12
 
 COPY . /src
 
@@ -12,4 +12,4 @@ FROM alpine:latest
 ENV VITASDK /home/user/vitasdk
 ENV PATH ${VITASDK}/bin:$PATH
 
-COPY --from=0 /src/build/vitasdk ${VITASDK}
+COPY --from=0 /src/build/vitasdk ${VITASDK}