Added explicit HOME and PATH environment vars to `npm install` tasks

iconv was refusing to compile:

    Error: node-gyp requires that the user's home directory is specified in either of the environmental variables HOME or USERPROFILE
        at new Gyp (/usr/lib/node_modules/npm/node_modules/node-gyp/lib/node-gyp.js:54:11)
        at gyp (/usr/lib/node_modules/npm/node_modules/node-gyp/lib/node-gyp.js:43:10)
        at Object.<anonymous> (/usr/lib/node_modules/npm/node_modules/node-gyp/bin/node-gyp.js:20:12)
        at Module._compile (module.js:456:26)
        at Object.Module._extensions..js (module.js:474:10)
        at Module.load (module.js:356:32)
        at Function.Module._load (module.js:312:12)
        at Function.Module.runMain (module.js:497:10)
        at startup (node.js:119:16)
        at node.js:906:3