fix: Add support for fish 2.6

Author: kylef

CHANGELOG.md

@@ -17,6 +17,7 @@
   3.1-dev and 4.0-dev.
 - When building Swift from source, swiftenv will download tarballs instead of
   git cloning the repository resulting in faster download speed.
+- Adds support for Fish 2.6.
 
 ## 1.2.1
 

docs/installation.md

@@ -33,8 +33,8 @@
     For Fish:
 
     ```shell
-    $ echo 'setenv SWIFTENV_ROOT "$HOME/.swiftenv"' >> ~/.config/fish/config.fish
-    $ echo 'setenv PATH "$SWIFTENV_ROOT/bin" $PATH' >> ~/.config/fish/config.fish
+    $ echo 'set -gx SWIFTENV_ROOT "$HOME/.swiftenv"' >> ~/.config/fish/config.fish
+    $ echo 'set -gx PATH "$SWIFTENV_ROOT/bin" $PATH' >> ~/.config/fish/config.fish
     $ echo 'if which swiftenv > /dev/null; status --is-interactive; and source (swiftenv init -|psub); end' >> ~/.config/fish/config.fish
     ```