use mississippi string library

The [mississippi](https://github.com/maxogden/mississippi) module ties together a bunch of utilities like pump, pumpify, etc, giving them consistent names and [documentation](https://github.com/maxogden/mississippi).   To make our code more consistent, I recommend using it whenever appropriate rather than using pump, pumpify, etc directly.

Author: Matt Zumwalt

lib/import.js

@@ -1,4 +1,4 @@
-var pump = require('pump')
+var miss = require('mississippi')
 var through = require('through2')
 var parseInputStream = require('parse-input-stream')
 
@@ -13,7 +13,7 @@ function importPipeline (jawn, opts, callback) {
   var parser = parseInputStream(opts)
   var transform = through.obj(stringifyData, end)
 
-  pump(parser, transform, writeStream, function done (err) {
+  miss.pipe(parser, transform, writeStream, function done (err) {
     callback(err, writeStream.id)
   })
 

package.json

@@ -24,9 +24,9 @@
     "fs": "0.0.2",
     "hypercore": "~1.8.0",
     "level": "~1.4.0",
+    "mississippi": "^1.2.0",
     "parse-input-stream": "^1.0.1",
     "path": "~0.12.7",
-    "pump": "^1.0.1",
     "tape": "~4.5.1",
     "through2": "^2.0.1"
   },