change javascript due to segfault in assets precompile

Gemfile

@@ -6,7 +6,7 @@ gem 'rails', '~>4'
 
 # execjs compatible javascript runtime
 gem 'execjs', '~>2.7.0'
-gem 'therubyracer', :platforms => :ruby
+gem 'duktape'
 
 gem 'devise', '~>4.4'
 gem 'cancancan', '~>1.10.1'

Gemfile.lock

@@ -165,6 +165,7 @@ GEM
       responders
       warden (~> 1.2.3)
     diff-lcs (1.4.4)
+    duktape (2.6.0.0)
     erubis (2.7.0)
     execjs (2.7.0)
     factory_girl (4.5.0)
@@ -218,7 +219,6 @@ GEM
       httparty
     libnotify (0.5.9)
       ffi (~> 1.0.0)
-    libv8 (3.16.14.19)
     listen (3.7.0)
       rb-fsevent (~> 0.10, >= 0.10.3)
       rb-inotify (~> 0.9, >= 0.9.10)
@@ -307,7 +307,6 @@ GEM
     rb-fsevent (0.11.0)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
-    ref (2.0.0)
     responders (2.4.1)
       actionpack (>= 4.2.0, < 6.0)
       railties (>= 4.2.0, < 6.0)
@@ -369,9 +368,6 @@ GEM
       net-scp (>= 1.1.2)
       net-ssh (>= 2.8.0)
     subexec (0.2.3)
-    therubyracer (0.12.3)
-      libv8 (~> 3.16.14.15)
-      ref
     thor (1.1.0)
     thread_safe (0.3.6)
     tilt (1.4.1)
@@ -411,6 +407,7 @@ DEPENDENCIES
   datagrid (~> 0.7.1)
   decent_exposure (~> 2.2.0)
   devise (~> 4.4)
+  duktape
   execjs (~> 2.7.0)
   factory_girl_rails (~> 4.5.0)
   fcgi (~> 0.9.2.1)
@@ -447,7 +444,6 @@ DEPENDENCIES
   sqlite3 (~> 1.3.6)
   squeel (~> 1.2.3)
   state_machine (~> 1.2.0)!
-  therubyracer
   turn (~> 0.9.6)
   uglifier (>= 1.3.0)