added flag

biopet.wdl

@@ -7,7 +7,7 @@ task FastqSplitter {
     command {
     mkdir -p ${sep=' ' prefix(outputPath + "/chunk_", range(numberChunks))}
     ${if (numberChunks > 1) then ("java -jar " + tool_jar + " -i " + inputFastq + write_lines(prefix("-o ", range(numberChunks))))
-    else ("ln -s " + inputFastq + " " + outputPath + "/chunk_0/" + basename(inputFastq))}
+    else ("ln -sf " + inputFastq + " " + outputPath + "/chunk_0/" + basename(inputFastq))}
     }
 
     output {