Fix compatibility with click version 8

In the new version of click, if an option has no type and
a default value is of type bool, the required value is also bool.

pipenv/cli/command.py

@@ -460,6 +460,7 @@ def run(state, command, args):
     "--unused",
     nargs=1,
     default=False,
+    type=click.types.STRING,
     help="Given a code path, show potentially unused dependencies.",
 )
 @option(

pipenv/cli/options.py

@@ -237,7 +237,8 @@ def callback(ctx, param, value):
         return value
     return option("--python", default=False, nargs=1, callback=callback,
                   help="Specify which version of Python virtualenv should use.",
-                  expose_value=False, allow_from_autoenv=False)(f)
+                  expose_value=False, allow_from_autoenv=False,
+                  type=click.types.STRING)(f)
 
 
 def pypi_mirror_option(f):
@@ -319,7 +320,8 @@ def callback(ctx, param, value):
             state.installstate.requirementstxt = value
         return value
     return option("--requirements", "-r", nargs=1, default=False, expose_value=False,
-                  help="Import a requirements.txt file.", callback=callback)(f)
+                  help="Import a requirements.txt file.", callback=callback,
+                  type=click.types.STRING)(f)
 
 
 def emit_requirements_flag(f):
@@ -360,7 +362,7 @@ def callback(ctx, param, value):
         return value
     return option("--code", "-c", nargs=1, default=False, help="Install packages "
                   "automatically discovered from import statements.", callback=callback,
-                  expose_value=False)(f)
+                  expose_value=False, type=click.types.STRING)(f)
 
 
 def deploy_option(f):