Add support for ruby-slim syntax

.gitmodules

@@ -227,3 +227,6 @@
 [submodule "assets/syntaxes/02_Extra/LLVM"]
 	path = assets/syntaxes/02_Extra/LLVM
 	url = https://github.com/ioncodes/LLVM.tmBundle
+[submodule "assets/syntaxes/02_Extra/Slim"]
+	path = assets/syntaxes/02_Extra/Slim
+	url = https://github.com/slim-template/ruby-slim.tmbundle.git

CHANGELOG.md

@@ -21,7 +21,7 @@
 - LLVM, see #1777 (@ioncodes)
 - Highlight for `vimrc` and `gvimrc` files, see #1763 (@SuperSandro2000)
 - Syslog highlighting improvements, see #1793 (@scop)
-
+- Added support for `slim` syntax, see #1693 (@mfinelli)
 
 ## New themes