Fix swapped variables in write_all_browser_files() (#1)

[SycamoreLeaf]

Variables fasta_fn and motif_descs are passed between three functions as follows:

_browser_files_main() --> write_all_browser_files() --> write_frac_wigs()

The two variables were swapped at both interfaces.

---

_browser_files_main() --> write_all_browser_files():

tombo/tombo/_text_output_commands.py

Lines 457 to 461 in afdb4d8

	write_all_browser_files(
	args.fast5_basedirs, args.control_fast5_basedirs, args.corrected_group,
	args.basecall_subgroups, args.statistics_filename,
	args.browser_file_basename, args.file_types, args.genome_fasta,
	args.motif_descriptions)

tombo/tombo/_text_output_commands.py

Lines 322 to 324 in afdb4d8

	def write_all_browser_files(
	fast5s_dirs, ctrl_fast5s_dirs, corr_grp, bc_subgrps,
	stats_fn, wig_base, wig_types, motif_descs, fasta_fn):

write_all_browser_files() --> write_frac_wigs():

tombo/tombo/_text_output_commands.py

Lines 383 to 386 in afdb4d8

	write_frac_wigs(
	all_stats, wig_base, FRAC_WIG_TYPE in wig_types,
	DFRAC_WIG_TYPE in wig_types, STAT_WIG_TYPE in wig_types,
	VCOV_WIG_TYPE in wig_types, motif_descs, fasta_fn)

tombo/tombo/_text_output_commands.py

Lines 95 to 97 in afdb4d8

	def write_frac_wigs(
	all_stats, wig_base, do_frac, do_damp, do_stats, do_vcov, fasta_fn,
	motif_descs):