Merge bitcoin#606: travis: Remove unused sudo:false

7667532 travis: Remove unused sudo:false (MarcoFalke)

Pull request description:

  Builds in sudo-disabled docker containers are no longer available as of last year and all builds happen on sudo enabled vms.

  Source: https://blog.travis-ci.com/2018-11-19-required-linux-infrastructure-migration#timeline---its-happening-fast

Tree-SHA512: 882585ba4e1596ad34ddf163acecd043da63443fa95653fba63b03dacf3a669128f1ed142527484cc8dab98de341b425425f418b8151cf7303b0e906ae259a9a

.travis.yml

@@ -1,5 +1,5 @@
 language: c
-sudo: false
+os: linux
 addons:
   apt:
     packages: libgmp-dev
@@ -66,4 +66,3 @@ script:
  - if [ -n "$HOST" ]; then export USE_HOST="--host=$HOST"; fi
  - if [ "x$HOST" = "xi686-linux-gnu" ]; then export CC="$CC -m32"; fi
  - ./configure --enable-experimental=$EXPERIMENTAL --enable-endomorphism=$ENDOMORPHISM --with-field=$FIELD --with-bignum=$BIGNUM --with-scalar=$SCALAR --enable-ecmult-static-precomputation=$STATICPRECOMPUTATION --enable-module-ecdh=$ECDH --enable-module-recovery=$RECOVERY --enable-jni=$JNI $EXTRAFLAGS $USE_HOST && make -j2 $BUILD
-os: linux