Use a different environment variable to run rustfmt check

By @Disasm

.travis.yml

@@ -23,7 +23,7 @@ matrix:
       language: bash
       if: (branch = staging OR branch = trying OR branch = master) OR (type = pull_request AND branch = master)
 
-    - env: RUSTFMT=1
+    - env: CHECK_RUSTFMT=1
       rust: stable
       if: (branch = staging OR branch = trying OR branch = master) OR (type = pull_request AND branch = master)
 

ci/install.sh

@@ -13,6 +13,6 @@ if [ -n "${CHECK_BLOBS:-}" ]; then
     fi
 fi
 
-if [ -n "${RUSTFMT:-}" ]; then
+if [ -n "${CHECK_RUSTFMT:-}" ]; then
     rustup component add rustfmt
 fi

ci/script.sh

@@ -15,6 +15,6 @@ if [ -n "${CHECK_BLOBS:-}" ]; then
     ./check-blobs.sh
 fi
 
-if [ -n "${RUSTFMT:-}" ]; then
+if [ -n "${CHECK_RUSTFMT:-}" ]; then
     cargo fmt -- --check
 fi