diff --git a/.travis.yml b/.travis.yml
index 50ae761..84e58fb 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,13 +1,13 @@
 cache:
   directories:
     - $HOME/.cache/rebar3
-    - $TRAVIS_BUILD_DIR/_build
 install: true
 language: erlang
 notifications:
   email: false
 otp_release:
-  - 20.1
+  - 21.0.3
+  - 20.3
   - 19.3
 script: "make travis"
 services:
diff --git a/rebar.config b/rebar.config
index cf73030..918d14a 100644
--- a/rebar.config
+++ b/rebar.config
@@ -14,7 +14,7 @@
   {murmur, ".*",
     {git, "https://github.com/lpgauth/murmur.git", {tag, "0.1.0"}}},
   {shackle, ".*",
-    {git, "https://github.com/lpgauth/shackle.git", {tag, "0.6.0"}}}
+    {git, "https://github.com/lpgauth/shackle.git", {tag, "0.6.2"}}}
 ]}.
 
 {edoc_opts, [
diff --git a/rebar.lock b/rebar.lock
index 9f1f10f..8e882f4 100644
--- a/rebar.lock
+++ b/rebar.lock
@@ -14,5 +14,5 @@
   0},
  {<<"shackle">>,
   {git,"https://github.com/lpgauth/shackle.git",
-       {ref,"d8a837c36f6e675e91b7e78f249f233c78f45cd5"}},
+       {ref,"1cf730d86b918df5d390dcfce7f33f49de8e2084"}},
   0}].