Downgrade event-stream package to 3.3.4

From the phosphor-webui alert:
"The NPM package flatmap-stream is considered malicious.
A malicious actor added this package as a dependency to the NPM
event-stream package in versions 3.3.6 and later. Users of
event-stream are encouraged to downgrade to the last non-malicious
version, 3.3.4."

More information can be found at:
https://github.com/dominictarr/event-stream/issues/116
https://arstechnica.com/information-technology/2018/11/hacker-backdoors-widely-used-open-source-software-to-steal-bitcoin/

Tested: Manually on a Witherspoon.
Change-Id: I2555ee04be69cc42f99cf3a5d18a99a4d5c26324
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>
diff --git a/package.json b/package.json
index 1536539..6e5db80 100644
--- a/package.json
+++ b/package.json
@@ -54,7 +54,7 @@
     "copy-webpack-plugin": "4.5.2",
     "css-loader": "1.0.0",
     "eslint-plugin-angular": "3.3.0",
-    "event-stream": "3.3.5",
+    "event-stream": "3.3.4",
     "file-loader": "2.0.0",
     "html-loader": "^0.5.5",
     "html-minifier": "^3.5.20",