Add mkdirp and rimraf devDeps

Browserify won't create necessary directories. So they need to be
created prior to running the builds. Which also means we need to use a
cross-platform `mkdir` command. And we need to run the clean command as
part of build/preparation so we need cross-platform rm-rf.

Author: jasonkarns

package.json

@@ -104,12 +104,14 @@
     "core-assert": "^0.2.1",
     "headerify": "^1.0.1",
     "is-number": "^3.0.0",
+    "mkdirp": "^0.5.1",
     "mocha": "^3.2.0",
     "mocha-given": "^0.1.3",
     "nyc": "^10.1.2",
     "power-assert": "^1.4.4",
     "pryjs": "^1.0.3",
     "require-globify": "^1.4.1",
+    "rimraf": "^2.6.2",
     "standard": "^10.0.2",
     "teenytest": "^5.0.2",
     "testdouble": "3.2.1",

yarn.lock

@@ -4075,6 +4075,12 @@ rimraf@2, rimraf@^2.2.8, rimraf@^2.3.3, rimraf@^2.4.3, rimraf@^2.4.4, rimraf@^2.
   dependencies:
     glob "^7.0.5"
 
+rimraf@^2.6.2:
+  version "2.6.2"
+  resolved "https://registry.yarnpkg.com/rimraf/-/rimraf-2.6.2.tgz#2ed8150d24a16ea8651e6d6ef0f47c4158ce7a36"
+  dependencies:
+    glob "^7.0.5"
+
 ripemd160@^1.0.0:
   version "1.0.1"
   resolved "https://registry.yarnpkg.com/ripemd160/-/ripemd160-1.0.1.tgz#93a4bbd4942bc574b69a8fa57c71de10ecca7d6e"
@@ -4924,6 +4930,10 @@ yargs@~3.10.0:
     decamelize "^1.0.0"
     window-size "0.1.0"
 
+yarn@^1.3.2:
+  version "1.3.2"
+  resolved "https://registry.yarnpkg.com/yarn/-/yarn-1.3.2.tgz#5939762581b5b4ddcd3418c0f6be42df3aee195f"
+
 yeast@0.1.2:
   version "0.1.2"
   resolved "https://registry.yarnpkg.com/yeast/-/yeast-0.1.2.tgz#008e06d8094320c372dbc2f8ed76a0ca6c8ac419"