Fixes infinite loop when rendering Ipynb Diffs

Upgrades ipynbdiff gem to 0.4.5, fixing edge cases
that would lead to infinite loops and potential
customer outages.

Changelog: fixed

Gemfile

@@ -542,4 +542,4 @@ gem 'ipaddress', '~> 0.8.3'
 
 gem 'parslet', '~> 1.8'
 
-gem 'ipynbdiff', '0.4.4'
+gem 'ipynbdiff', '0.4.5'

Gemfile.lock

@@ -655,7 +655,7 @@ GEM
     invisible_captcha (1.1.0)
       rails (>= 4.2)
     ipaddress (0.8.3)
-    ipynbdiff (0.4.4)
+    ipynbdiff (0.4.5)
       diffy (~> 3.3)
       json (~> 2.5, >= 2.5.1)
     jaeger-client (1.1.0)
@@ -1536,7 +1536,7 @@ DEPENDENCIES
   icalendar
   invisible_captcha (~> 1.1.0)
   ipaddress (~> 0.8.3)
-  ipynbdiff (= 0.4.4)
+  ipynbdiff (= 0.4.5)
   jira-ruby (~> 2.1.4)
   js_regex (~> 3.7)
   json (~> 2.5.1)