chore: run circle as non-root user (#120)

Author: alexander-fenster

.circleci/config.yml

@@ -5,8 +5,7 @@ unit_tests: &unit_tests
     - checkout
     - run:
         name: Install modules and dependencies.
-# '--unsafe-perm' required as per https://github.com/grpc/grpc/issues/8941
-        command: npm install  --unsafe-perm
+        command: npm install
     - run:
         name: Install codecov.
         command: npm install codecov
@@ -86,27 +85,33 @@ jobs:
   node4:
     docker:
       - image: node:4
+        user: node
     <<: *unit_tests
   node6:
     docker:
       - image: node:6
+        user: node
     <<: *unit_tests
   node7:
     docker:
       - image: node:7
+        user: node
     <<: *unit_tests
   node8:
     docker:
       - image: node:8
+        user: node
     <<: *unit_tests
   node9:
     docker:
       - image: node:9
+        user: node
     <<: *unit_tests
 
   lint:
     docker:
       - image: node:8
+        user: node
     steps:
       - checkout
       - run:
@@ -119,6 +124,7 @@ jobs:
   docs:
     docker:
       - image: node:8
+        user: node
     steps:
       - checkout
       - run:
@@ -131,6 +137,7 @@ jobs:
   system_tests:
     docker:
       - image: node:8
+        user: node
     steps:
       - checkout
       - run:
@@ -159,6 +166,7 @@ jobs:
   publish_npm:
     docker:
       - image: node:8
+        user: node
     steps:
       - checkout
       - run: