Correct install_viewer.sh version in docs (rust-lang#1114)

Author: samestep

docs/src/install-guide.md

@@ -27,7 +27,7 @@ cd kani
 git submodule update --init
 ./scripts/setup/ubuntu/install_deps.sh
 ./scripts/setup/ubuntu/install_cbmc.sh
-./scripts/setup/install_viewer.sh 2.10
+./scripts/setup/install_viewer.sh 2.11
 ./scripts/setup/install_rustup.sh
 source $HOME/.cargo/env
 ```
@@ -43,7 +43,7 @@ cd kani
 git submodule update --init
 ./scripts/setup/macos-10.15/install_deps.sh
 ./scripts/setup/macos-10.15/install_cbmc.sh
-./scripts/setup/install_viewer.sh 2.10
+./scripts/setup/install_viewer.sh 2.11
 ./scripts/setup/install_rustup.sh
 source $HOME/.cargo/env
 ```