use "canvas" module_name for node-pre-gyp

See Automattic/node-canvas#1347

Fixes #72

Author: chearon

ci/tarball.sh

@@ -2,8 +2,8 @@
 CANVAS_PREBUILT_VERSION=$1
 FILENAME=$(
   node -e "
-    var p = process, v = p.versions, pkg = require('./package.json'), libc = require('detect-libc').family || 'unknown';
-    console.log([pkg.name, 'v$CANVAS_PREBUILT_VERSION', 'node-v' + v.modules, p.platform, libc, p.arch].join('-'));
+    var p = process, v = p.versions, libc = require('detect-libc').family || 'unknown';
+    console.log(['canvas', 'v$CANVAS_PREBUILT_VERSION', 'node-v' + v.modules, p.platform, libc, p.arch].join('-'));
   "
 ).tar.gz;