Upgrade npm to v4.6.1

Dockerfile

@@ -17,7 +17,7 @@ ENV NODE_VERSION ${NODE_VERSION:-v4.8.1}
 ENV METEOR_RELEASE ${METEOR_RELEASE:-1.4.4.1}
 ENV USE_EDGE ${USE_EDGE:-false}
 ENV METEOR_EDGE ${METEOR_EDGE:-1.5-beta.17}
-ENV NPM_VERSION ${NPM_VERSION:-4.5.0}
+ENV NPM_VERSION ${NPM_VERSION:-4.6.1}
 ENV ARCHITECTURE ${ARCHITECTURE:-linux-x64}
 ENV SRC_PATH ${SRC_PATH:-./}