rename version variables

Author: michaelgrund

pygmt/__init__.py

@@ -134,10 +134,10 @@ def _get_ghostscript_version():
 
         for gs_cmd in cmds:
             try:
-                version = subprocess.check_output(
+                gs_version = subprocess.check_output(
                     [gs_cmd, "--version"], universal_newlines=True
                 ).strip()
-                return version
+                return gs_version
             except FileNotFoundError:
                 continue
         return None
@@ -147,10 +147,10 @@ def _get_gmt_version():
         Get GMT version.
         """
         try:
-            version = subprocess.check_output(
+            gmt_version = subprocess.check_output(
                 ["gmt", "--version"], universal_newlines=True
             ).strip()
-            return version
+            return gmt_version
         except FileNotFoundError:
             return None