handle bad package names more gracefully

pipenv/cli.py

@@ -415,6 +415,8 @@ def proper_case(package_name):
 
     # Hit the simple API.
     r = requests.get('{0}/{1}'.format(project.source['url'], package_name))
+    if not r.ok:
+        raise IOError('Unable to find package {0} in PyPI repository.'.format(crayons.green(package_name)))
 
     # Parse the HTML.
     parser = SimpleHTMLParser()
@@ -528,7 +530,11 @@ def install(package_name=False, more_packages=False, dev=False, three=False, sys
 
         # Proper-case incoming package name (check against API).
         old_name = [k for k in convert_deps_from_pip(package_name).keys()][0]
-        new_name = proper_case(old_name)
+        try:
+            new_name = proper_case(old_name)
+        except IOError as e:
+            click.echo('{0} {1}'.format(crayons.red('Error: '), e.args[0], crayons.green(package_name)))
+            continue
         package_name = package_name.replace(old_name, new_name)
 
         click.echo('Installing {0}...'.format(crayons.green(package_name)))