Revert "Update html2canvas version"

This reverts commit c9a60c4.

# Conflicts:
#	www/package-lock.json
#	www/package.json

Author: niklasvh

www/package-lock.json

@@ -18,7 +18,7 @@
     "gatsby-source-filesystem": "^1.5.9",
     "gatsby-transformer-remark": "^1.7.23",
     "gzip-size": "^4.1.0",
-    "html2canvas": "^1.0.0-alpha.9",
+    "html2canvas": "1.0.0-alpha.4",
     "mkdirp": "^0.5.1",
     "typography": "^0.16.6",
     "typography-theme-github": "^0.15.10"