travis.yml: fix GCOV setting

1. GCOV=0 is wrong, it should be left unset (or set to empty value)
2. GCOV=1 only makes sense for TR_ARCH=local, others are not using it
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

.travis.yml

@@ -5,12 +5,12 @@ services:
   - docker
 env:
   - TR_ARCH=local       GCOV=1
-  - TR_ARCH=local       GCOV=0  CLANG=1
-  - TR_ARCH=x86_64      GCOV=1
-  - TR_ARCH=armv7hf     GCOV=1
-  - TR_ARCH=aarch64     GCOV=1
-  - TR_ARCH=ppc64le     GCOV=1
-  - TR_ARCH=alpine      GCOV=1
+  - TR_ARCH=local       CLANG=1
+  - TR_ARCH=x86_64
+  - TR_ARCH=armv7hf
+  - TR_ARCH=aarch64
+  - TR_ARCH=ppc64le
+  - TR_ARCH=alpine
 script:
   - sudo make -C scripts/travis $TR_ARCH
 after_success: