build: align minimum clang dependency with ndn-cxx

ndn-cxx requires clang 6 or later, so there's no point
supporting older versions in ndn-tools

Change-Id: I7be683abd4fce12c85187c0b5abf2ee288bbe908
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index d9f98d8..47d9a6a 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -22,8 +22,6 @@
         include:
           - compiler: g++-7
             os: ubuntu-18.04
-          - compiler: clang++-5.0
-            os: ubuntu-18.04
           - compiler: clang++-6.0
             os: ubuntu-18.04
     runs-on: ${{ matrix.os }}
@@ -37,7 +35,7 @@
           sudo apt-get -qy install ${CXX/clang++/clang}
           ${CXX} --version
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
       - name: Build and test
         run: ./.jenkins
 
@@ -63,6 +61,6 @@
         with:
           xcode-version: ${{ matrix.xcode }}
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
       - name: Build and test
         run: ./.jenkins
diff --git a/.github/workflows/docs.yml b/.github/workflows/docs.yml
index f94c307..a5b4c30 100644
--- a/.github/workflows/docs.yml
+++ b/.github/workflows/docs.yml
@@ -21,7 +21,7 @@
       WAF_JOBS: 3
     steps:
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
       - name: Install dependencies
         run: |
           case ${RUNNER_OS} in
diff --git a/.waf-tools/default-compiler-flags.py b/.waf-tools/default-compiler-flags.py
index 53f0f8c..7c6d282 100644
--- a/.waf-tools/default-compiler-flags.py
+++ b/.waf-tools/default-compiler-flags.py
@@ -28,9 +28,9 @@
             elif ccver < (11, 0, 0):
                 warnmsg = ('Using a version of Xcode older than 11.3 is not '
                            'officially supported and may result in build failures.')
-        elif ccver < (5, 0, 0):
+        elif ccver < (6, 0, 0):
             errmsg = ('The version of clang you are using is too old.\n'
-                      'The minimum supported clang version is 5.0.')
+                      'The minimum supported clang version is 6.0.')
         conf.flags = ClangFlags()
     else:
         warnmsg = '%s compiler is unsupported' % cxx
@@ -213,8 +213,6 @@
                               '-Wundefined-func-template',
                               '-Wno-unused-local-typedef', # Bugs #2657 and #3209
                               ]
-        if self.getCompilerVersion(conf) < (6, 0, 0):
-            flags['CXXFLAGS'] += ['-Wno-missing-braces'] # Bug #4721
         return flags
 
     def getOptimizedFlags(self, conf):
@@ -223,6 +221,4 @@
                               '-Wundefined-func-template',
                               '-Wno-unused-local-typedef', # Bugs #2657 and #3209
                               ]
-        if self.getCompilerVersion(conf) < (6, 0, 0):
-            flags['CXXFLAGS'] += ['-Wno-missing-braces'] # Bug #4721
         return flags
diff --git a/manpages/conf.py b/manpages/conf.py
index 262a32a..7c3ea95 100644
--- a/manpages/conf.py
+++ b/manpages/conf.py
@@ -18,7 +18,7 @@
 # -- Project information -----------------------------------------------------
 
 project = u'NDN Essential Tools'
-copyright = u'Copyright © 2014-2021 Named Data Networking Project.'
+copyright = u'Copyright © 2014-2022 Named Data Networking Project.'
 author = u'Named Data Networking Project'
 
 # The short X.Y version.