downgrade max gcc to 15, gcc 16 not yet released

Signed-off-by: DONNOT Benjamin <[email protected]>

Author: BDonnot

.circleci/config.yml

@@ -7,10 +7,10 @@ orbs:
 executors:
     gcc_latest:
         docker:
-            - image: gcc:16
+            - image: gcc:15
     gcc_prev_latest:
         docker:
-            - image: gcc:15
+            - image: gcc:14
     gcc_earliest:
         docker:
             - image: gcc:8

README.md

@@ -282,13 +282,13 @@ cd ..
 
 Some tests are performed automatically on standard platform each time modifications are made in the lightsim2grid code.
 
-These tests include, for now, compilation on gcc (version 8, 12 and 13) and clang (version 11, 16 and 17).
+These tests include, for now, compilation on gcc (version 8, 14 and 15) and clang (version 11, 20 and 21).
 
 **NB** Intermediate versions of clang and gcc (*eg* gcc 9 or clang 12) are not tested regularly, but lightsim2grid used to work on these. 
-We suppose that if it works on *eg* clang 10 and clang 14 then it compiles also on all intermediate versions.
+We suppose that if it works on *eg* clang 11 and clang 21 then it compiles also on all intermediate versions.
 
 **NB** Package might work (we never tested it) on earlier version of these compilers. 
-The only "real" requirement for lightsim2grid is to have a compiler supporting c++11
+The only "real" requirement for lightsim2grid is to have a compiler supporting c++14
 (at least).
 
 ### Known issues