Allow for adding requirements objects directly to pipfile

Signed-off-by: Dan Ryan <dan@danryan.co>

pipenv/core.py

@@ -1908,7 +1908,7 @@ def do_install(
             )
             # Add the package to the Pipfile.
             try:
-                project.add_package_to_pipfile(pkg_requirement.as_line(), dev)
+                project.add_package_to_pipfile(pkg_requirement, dev)
             except ValueError as e:
                 click.echo(
                     "{0} {1}".format(crayons.red("ERROR (PACKAGE NOT INSTALLED):"), e)

pipenv/project.py

@@ -770,13 +770,14 @@ def remove_package_from_pipfile(self, package_name, dev=False):
             del p[key][name]
             self.write_toml(p)
 
-    def add_package_to_pipfile(self, package_name, dev=False):
+    def add_package_to_pipfile(self, package, dev=False):
         from .vendor.requirementslib import Requirement
 
         # Read and append Pipfile.
         p = self.parsed_pipfile
         # Don't re-capitalize file URLs or VCSs.
-        package = Requirement.from_line(package_name.strip())
+        if not isinstance(package, Requirement):
+            package = Requirement.from_line(package.strip())
         _, converted = package.pipfile_entry
         key = "dev-packages" if dev else "packages"
         # Set empty group if it doesn't exist yet.