Make the CKM matrix into a string for yadism

[scarlehoff]

yadism asks for a string for the CKM Matrix, while we have many runcards where the CKM is really a list. This PR just makes the change before passing the theory card to yadism

@evagroenendijk if you try to run some of the DIS datasets they will fail depending on the runcard you use, just so that you are aware.

Below a runcard that works with this PR and doesn't without (it's a minimal change to avoid having to have several versions of the same runcards).

`theory.yaml`

``` CKM: - 0.97428 - 0.2253 - 0.00347 - 0.2252 - 0.97345 - 0.041 - 0.00862 - 0.0403 - 0.999152 Comments: NNLO nFONLL theory. Equivalent to 700/708. 4.0 baseline. DAMP: 0 DAMPPOWERb: null DAMPPOWERc: null EScaleVar: null FNS: FONLL-FFNS FONLLParts: full GF: 1.1663787e-05 HQ: POLE IC: 1 ID: 4000000000 IterEv: null MP: 0.938 MW: 80.398 MZ: 91.1876 MaxNfAs: null MaxNfPdf: 5 ModEv: TRN ModSV: null NfFF: 3 PTO: 2 PTODIS: null PTOEKO: 2 Q0: 1.65 QED: 0 Qedref: null Qmb: 4.92 Qmc: 1.51 Qmt: 172.5 Qref: 91.2 SIN2TW: 0.23126 SxOrd: null SxRes: null TMC: 1 XIF: 1.0 XIR: 1.0 alphaqed: 0.0077553 alphas: 0.118 global_nx: null kbThr: 1.0 kcThr: 1.0 ktThr: 1.0 mb: 4.92 mc: 1.51 mt: 172.5 n3lo_ad_variation: - 0 - 0 - 0 - 0 - 0 - 0 - 0 n3lo_cf_variation: 0 nf0: 4 nfref: 5 use_fhmruvv: false ```

[felixhekhorn]

This is complementary to https://github.com/NNPDF/yadism/pull/309 - not sure if we want to do both ...

[scarlehoff]

Ah, probably let's just update the master branch to the new version of yadism.

@evagroenendijk Make sure you are using the version of yadism from the master branch of the yadism repository.