Remove dependency on path-is-absolute

Per https://www.npmjs.com/package/path-is-absolute:

> This package is no longer relevant as Node.js 0.12 is unmaintained.

PR-URL: #477
Credit: @jsha
Close: #477
Reviewed-by: @isaacs

test/nodir.js

@@ -2,15 +2,14 @@ require("./global-leakage.js")
 var test = require("tap").test
 var glob = require('../')
 var path = require('path')
-var isAbsolute = require('path-is-absolute')
 process.chdir(__dirname + '/fixtures')
 
 function cacheCheck(g, t) {
   // verify that path cache keys are all absolute
   var caches = [ 'cache', 'statCache', 'symlinks' ]
   caches.forEach(function (c) {
     Object.keys(g[c]).forEach(function (p) {
-      t.ok(isAbsolute(p), p + ' should be absolute')
+      t.ok(path.isAbsolute(p), p + ' should be absolute')
     })
   })
 }

test/root-nomount.js

@@ -2,14 +2,13 @@ require("./global-leakage.js")
 var tap = require("tap")
 var glob = require('../')
 var path = require('path')
-var isAbsolute = require('path-is-absolute')
 
 function cacheCheck(g, t) {
   // verify that path cache keys are all absolute
   var caches = [ 'cache', 'statCache', 'symlinks' ]
   caches.forEach(function (c) {
     Object.keys(g[c]).forEach(function (p) {
-      t.ok(isAbsolute(p), p + ' should be absolute')
+      t.ok(path.isAbsolute(p), p + ' should be absolute')
     })
   })
 }

test/root.js

@@ -5,14 +5,13 @@ process.chdir(__dirname + '/fixtures')
 
 var glob = require('../')
 var path = require('path')
-var isAbsolute = require('path-is-absolute')
 
 function cacheCheck(g, t) {
   // verify that path cache keys are all absolute
   var caches = [ 'cache', 'statCache', 'symlinks' ]
   caches.forEach(function (c) {
     Object.keys(g[c]).forEach(function (p) {
-      t.ok(isAbsolute(p), p + ' should be absolute')
+      t.ok(path.isAbsolute(p), p + ' should be absolute')
     })
   })
 }