Travis-CI: disable macOS and documentation builds

Temporarily disable unnecessary builds for trouble shooting with
  Travis-CI support (no Credits)

.travis.yml

@@ -1,4 +1,3 @@
-sudo: required
 dist: xenial
 osx_image: xcode12.2
 
@@ -6,11 +5,10 @@ cache: ccache
 
 language:
   - c++
-# - objective-c
 
 os:
   - linux
-  - osx
+  ## disabled:  - osx
 
 compiler:
   - gcc
@@ -25,7 +23,7 @@ matrix:
   include:
     os: linux
     compiler: clang
-    env: ANALYZE=true DOC=true
+    ## env: ANALYZE=true DOC=true
 
 branches:
   only:
@@ -51,20 +49,32 @@ before_script:
 
 script:
   - |
-   if [ $ANALYZE = "false" ]; then
-     autoconf
-     ./configure
-     make
-     mkdir cmake-build
-     cd cmake-build
-     cmake -G "Unix Makefiles" -D FLTK_BUILD_EXAMPLES=ON ..
-     make
-   else
-     mkdir scan-build
-     cd scan-build
-     scan-build cmake -G "Unix Makefiles" -D FLTK_BUILD_EXAMPLES=ON ..
-     scan-build -v make
-   fi
+    if [ $ANALYZE = "false" ]; then
+      echo
+      echo "start configure/make at `date`"
+      echo
+      autoconf
+      ./configure
+      make
+      echo
+      echo "start CMake/make at `date`"
+      echo
+      mkdir cmake-build
+      cd cmake-build
+      cmake -G "Unix Makefiles" -D FLTK_BUILD_EXAMPLES=ON ..
+      make
+    else
+      echo
+      echo "start scan-build/make at `date`"
+      echo
+      mkdir scan-build
+      cd scan-build
+      scan-build cmake -G "Unix Makefiles" -D FLTK_BUILD_EXAMPLES=ON ..
+      scan-build -v make
+    fi
+    echo
+    echo "done at `date`"
+    echo
 
 after_success:
   - |
@@ -75,12 +85,4 @@ after_success:
       cd -
     fi
 
-# explicit email notifications don't play well with forks: don't use them
-# default: committer and author get notifications
-# we're now using defaults for everything, hence settings are commented
-# out, left only for documentation purposes...
-
-#notifications:
-#  email:
-#    on_success: change # default: change, may be: never
-#    on_failure: always # default: always
+# use default email notification: committer and author get notifications