Travis CI: Run distcheck on focal with automake-1.16.5

New tools version to prepare distributive tarball:
* autoconf-2.69
* automake-1.16.5 (updated from 1.15)
* m4-1.4.18
* libtool-2.4.6 (needed to build automake)

Also, remove --no-check-certificate for downloads from ftp.gnu.org.

.travis.yml

@@ -603,10 +603,10 @@ jobs:
     - CROSS_GCC_VER=4.6.2
     - NOLIBC_ARCH_ABI=tilegx-linux
     - NOLIBC_DELIM=_
-  - env:
+  - dist: focal
+    env:
     - MAKEFILE_TARGET=distcheck
-    - AUTOMAKE_VER=1.15
-    - M4_VER=1.4.18
+    - AUTOMAKE_VER=1.16.5
     - LIBTOOL_VER=2.4.6
 
 before_install:
@@ -634,17 +634,17 @@ before_install:
   fi
 - if [[ "$M4_VER" != "" ]]; then
     M4_XZ_URL=$GNU_DOWNLOAD_SITE/m4/m4-$M4_VER.tar.xz;
-    wget --no-check-certificate -O - $M4_XZ_URL | tar xf - --xz --directory ~;
+    wget -O - $M4_XZ_URL | tar xf - --xz --directory ~;
     (cd ~/m4-$M4_VER && ./configure --prefix=$GNUTOOLS_ROOT && make -j check && make install);
   fi
 - if [[ "$LIBTOOL_VER" != "" ]]; then
     LIBTOOL_XZ_URL=$GNU_DOWNLOAD_SITE/libtool/libtool-$LIBTOOL_VER.tar.xz;
-    wget --no-check-certificate -O - $LIBTOOL_XZ_URL | tar xf - --xz --directory ~;
+    wget -O - $LIBTOOL_XZ_URL | tar xf - --xz --directory ~;
     (cd ~/libtool-$LIBTOOL_VER && ./configure --prefix=$GNUTOOLS_ROOT && make -j && make install);
   fi
 - if [[ "$AUTOMAKE_VER" != "" ]]; then
     AUTOMAKE_XZ_URL=$GNU_DOWNLOAD_SITE/automake/automake-$AUTOMAKE_VER.tar.xz;
-    wget --no-check-certificate -O - $AUTOMAKE_XZ_URL | tar xf - --xz --directory ~;
+    wget -O - $AUTOMAKE_XZ_URL | tar xf - --xz --directory ~;
     (cd ~/automake-$AUTOMAKE_VER && ./configure --prefix=$GNUTOOLS_ROOT && make -j && make install);
   fi
 - if [[ "$MAKEFILE_TARGET" == "dist"* ]]; then