Make `presubmit.sh` work from `.fuchsia` directory

The current script failed to enter the 'web' directory.
Also use `set -i` to exit of first failure in a more readable way.

Change-Id: I1c752abc87f7a5b6312b539208b2bb8b4333986a

presubmit.sh

diff --git a/presubmit.sh b/presubmit.sh
index 1de98be..a225944 100755
--- a/presubmit.sh
+++ b/presubmit.sh
@@ -1,30 +1,35 @@
 #!/bin/sh
+set -e  # Exit on first error.
+cd $( dirname "${BASH_SOURCE[0]}" )
 
-echo "Checking benches..." && \
-RUSTFLAGS="-D warnings" cargo check -q -p benches && \
-echo "Checking demo..." && \
-RUSTFLAGS="-D warnings" cargo check -q -p demo && \
-echo "Checking conveyor-sort..." && \
-RUSTFLAGS="-D warnings" cargo check -q -p conveyor-sort && \
-echo "Checking painter..." && \
-RUSTFLAGS="-D warnings" cargo check -q -p painter && \
-echo "Checking pristine..." && \
-RUSTFLAGS="-D warnings" cargo check -q -p pristine && \
-echo "Checking renderer..." && \
-RUSTFLAGS="-D warnings" cargo check -q -p renderer && \
-echo "Checking web..." && \
-cd web && RUSTFLAGS="-D warnings -C target-feature=+simd128,+atomics,+bulk-memory,+mutable-globals" wasm-pack -q build --target web && cd .. && \
-echo "Testing conveyor-sort..." && \
-cargo test -q -p conveyor-sort && \
-echo "Testing painter..." && \
-cargo test -q -p painter && \
-echo "Testing renderer..." && \
-cargo test -q -p renderer && \
-echo "Checking formatting..." && \
-cargo fmt -q --check && \
-echo "Checking docs..." && \
-RUSTDOCFLAGS="-D warnings" cargo doc -q -p forma && \
-echo "Running forma doc tests..." && \
-cargo test -q --doc -p forma && \
-echo && \
+echo "Checking benches..."
+RUSTFLAGS="-D warnings" cargo check -q -p benches
+echo "Checking demo..."
+RUSTFLAGS="-D warnings" cargo check -q -p demo
+echo "Checking conveyor-sort..."
+RUSTFLAGS="-D warnings" cargo check -q -p conveyor-sort
+echo "Checking painter..."
+RUSTFLAGS="-D warnings" cargo check -q -p painter
+echo "Checking pristine..."
+RUSTFLAGS="-D warnings" cargo check -q -p pristine
+echo "Checking renderer..."
+RUSTFLAGS="-D warnings" cargo check -q -p renderer
+echo "Checking web..."
+(
+    cd web 
+    RUSTFLAGS="-D warnings -C target-feature=+simd128,+atomics,+bulk-memory,+mutable-globals" wasm-pack -q build --target web
+)
+echo "Testing conveyor-sort..."
+cargo test -q -p conveyor-sort
+echo "Testing painter..."
+cargo test -q -p painter
+echo "Testing renderer..."
+cargo test -q -p renderer
+echo "Checking formatting..."
+cargo fmt -q --check
+echo "Checking docs..."
+RUSTDOCFLAGS="-D warnings" cargo doc -q -p forma
+echo "Running forma doc tests..."
+cargo test -q --doc -p forma
+echo
 echo "Pre-submit passed successfully."