Upgrade Slate, point plugin to branch instead of hash

yarn.lock

@@ -8019,7 +8019,7 @@ slate-collapse-on-escape@^0.2.1:
   dependencies:
     to-pascal-case "^1.0.0"
 
-slate-drop-or-paste-images@tommoor/slate-drop-or-paste-images#f599369ab83bed60f4a804d553d7889716bf9ec1:
+slate-drop-or-paste-images@tommoor/slate-drop-or-paste-images#dev:
   version "0.5.0"
   resolved "https://codeload.github.com/tommoor/slate-drop-or-paste-images/tar.gz/f599369ab83bed60f4a804d553d7889716bf9ec1"
   dependencies:
@@ -8066,11 +8066,10 @@ slate-trailing-block@^0.2.4:
   version "0.2.4"
   resolved "https://registry.yarnpkg.com/slate-trailing-block/-/slate-trailing-block-0.2.4.tgz#6ce9525fa15f9f098d810d9312a4267799cd0e12"
 
-slate@^0.19.30:
-  version "0.19.30"
-  resolved "https://registry.yarnpkg.com/slate/-/slate-0.19.30.tgz#6c28a7ef53fd48d445c13c6037d39b96efacc22a"
+slate@^0.21.4:
+  version "0.21.4"
+  resolved "https://registry.yarnpkg.com/slate/-/slate-0.21.4.tgz#ae6113379cd838b7ec68ecd94834ce9741bc36f3"
   dependencies:
-    cheerio "^0.22.0"
     debug "^2.3.2"
     direction "^0.1.5"
     es6-map "^0.1.4"
@@ -8081,6 +8080,7 @@ slate@^0.19.30:
     is-in-browser "^1.1.3"
     is-window "^1.0.2"
     keycode "^2.1.2"
+    lodash "^4.17.4"
     prop-types "^15.5.8"
     react-portal "^3.1.0"
     selection-is-backward "^1.0.0"