Fixed typo in the rule read_length_histogram that caused crashing the pipeline.

snakemake/process_data/Snakefile

@@ -244,7 +244,7 @@ rule read_length_histogram:
 	shell:
 		"(python scripts/plot_read_lengths.py \
 		--sam {input.sam} \
-		--outdir {params.dir}) & > {log}"
+		--outdir {params.dir}) &> {log}"
 
 ################################################################################
 ### Count reads