FastQC/Dockerfile: add perl version

src/docker_modules/FastQC/0.11.5/Dockerfile

@@ -3,7 +3,7 @@ MAINTAINER Laurent Modolo
 
 ENV FASTQC_VERSION=0.11.5
 ENV PACKAGES fastqc=${FASTQC_VERSION}* \
-		perl
+		perl=5.26*
 
 RUN apt-get update && \
     apt-get install -y --no-install-recommends ${PACKAGES} && \