install-node: hardcode the path for npm.

This replaces nvm in npm-wrapper by harcoding the path the way we do
with node.  The main benefit is that this saves a few hundred
milliseconds every time we invoke npm.

scripts/lib/install-node

@@ -11,6 +11,7 @@ source "$NVM_DIR/nvm.sh"
 node_version=6.6.0
 nvm install "$node_version" && nvm alias default "$node_version"
 export NODE_BIN="$(nvm which default)"
+export NPM_BIN=$(echo "$NODE_BIN" | sed 's/node$/npm/')
 
 # Fix messed-up uid=500 and group write bits produced by nvm
 n=$(which node)
@@ -22,3 +23,4 @@ chmod -R go-w "$n"
 cp "$ZULIP_PATH/../../scripts/setup/node-wrapper" /usr/local/bin/node
 sed -i "s|NODE_PATH|$NODE_BIN|" /usr/local/bin/node
 cp "$ZULIP_PATH/../../scripts/setup/npm-wrapper" /usr/local/bin/npm
+sed -i "s|NPM_PATH|$NPM_BIN|" /usr/local/bin/npm

scripts/setup/npm-wrapper

@@ -1,4 +1,2 @@
 #!/bin/bash
-export NVM_DIR="/usr/local/nvm"
-[ -e "$NVM_DIR/nvm.sh" ] && . "$NVM_DIR/nvm.sh"
-npm "$@"
+NPM_PATH "$@"