fix trailing space

README.md

@@ -30,7 +30,7 @@ In your environment which has spectral-cluster-supertree installed:
 scs -i SOURCE_TREE_FILE -o SUPERTREE_FILE -p PCG_WEIGHTING_STRATEGY
 ```
 
-The ```-i``` and ```-o``` options for the input and output files are required. 
+The ```-i``` and ```-o``` options for the input and output files are required.
 
 The ```-p``` *proper cluster graph* weighting strategy option must be one of ```ONE|DEPTH|BRANCH```. It defaults to ```BRANCH``` when not provided (not recommended when some trees are missing branch lenghts - see below).