v1.8 bump prior to GitHub+Zenodo release

I have not tested if it still works with Python 2. Not changing this here, so will patch if we do.

Author: awickert

setup.py

@@ -5,7 +5,7 @@
 
 setuptools.setup(
     name="GRLP",
-    version="1.7.0",
+    version="1.8.0",
     author="Andrew D. Wickert",
     author_email="[email protected]",
     description="Evolves gravel-bed river long profiles",