Require grainstore-0.10.7 to enhance marker type transform (2.0 -> 2.1)

See https://github.com/Vizzuality/grainstore/blob/0.10.7/NEWS.md

npm-shrinkwrap.json

@@ -182,7 +182,7 @@
       "version": "1.3.3"
     },
     "grainstore": {
-      "version": "0.10.6",
+      "version": "0.10.7",
       "dependencies": {
         "carto": {
           "version": "0.9.3-cdb2",

package.json

@@ -21,7 +21,7 @@
         "cluster2": "git://github.com/CartoDB/cluster2.git#cdb_production",
         "node-varnish": "0.1.1",
         "underscore"  : "~1.3.3",
-        "grainstore"  : "~0.10.6",
+        "grainstore"  : "~0.10.7",
         "windshaft"  : "~0.8.0",
         "step": "0.0.x",
         "generic-pool": "1.0.x",