escalate the activate() method

Close #204

news/204.bugfix

+Fix a bug that distributions are not removed in parallel mode.

pdm/installers/installers.py

@@ -83,7 +83,6 @@ class Installer:  # pragma: no cover
             ireq = pip_shims.install_req_from_line(dist.project_name)
         ireq.req = req
 
-        with self.environment.activate():
-            pathset = ireq.uninstall(auto_confirm=self.auto_confirm)
-            if pathset:
-                pathset.commit()
+        pathset = ireq.uninstall(auto_confirm=self.auto_confirm)
+        if pathset:
+            pathset.commit()

pdm/installers/synchronizers.py

@@ -285,7 +285,7 @@ class Synchronizer:
                     )
                 )
 
-        with stream.logging("install"):
+        with stream.logging("install"), self.environment.activate():
             with stream.indent("  "):
                 for job in sequential_jobs:
                     kind, key = job