Fix table column alignment for ratio values

The ljust padding in format_ratio added trailing spaces to reserve room
for significance symbols, but these spaces were then stripped by rstrip
in the table formatter's format_row, causing the last column to lose its
right-alignment.

This was exposed by #492 which made pval nil when --pvalue is not passed,
meaning the significance symbol is always empty in the common case, yet
the ljust padding was still applied and then stripped.

Remove the ljust padding entirely and let the table formatter handle
column alignment, restoring the original format_ratio logic.

Author: k0kubun

lib/results_table_builder.rb

@@ -214,8 +214,7 @@ def gc_ratio(base, other)
   def format_ratio(ratio, pval)
     sym = significance_symbol(pval)
     formatted = "%.3f" % ratio
-    suffix = sym.empty? ? "" : " (#{sym})"
-    (formatted + suffix).ljust(formatted.length + 6)
+    sym.empty? ? formatted : "#{formatted} (#{sym})"
   end
 
   def format_p_value(pval)