Fix Salesforce Web "spawn git ENOENT" build error

[INFO] Building Nuxeo Salesforce Web 8.10
[INFO] ------------------------------------------------------------------------
     [exec] Stack trace:
     [exec] Error: spawn git ENOENT
     [exec]     at exports._errnoException (util.js:907:11)
     [exec]     at Process.ChildProcess._handle.onexit (internal/child_process.js:178:32)
     [exec]     at onErrorNT (internal/child_process.js:344:16)
     [exec]     at nextTickCallbackWith2Args (node.js:442:9)
     [exec]     at process._tickCallback (node.js:356:17)
     [exec] 
     [exec] Console trace:
     [exec] Trace
     [exec]     at StandardRenderer.error (/opt/build/tools/node-v4.5.0-linux-x64/lib/node_modules/bower/lib/renderers/StandardRenderer.js:82:17)
     [exec]     at Logger. (/opt/build/tools/node-v4.5.0-linux-x64/lib/node_modules/bower/bin/bower:110:22)
     [exec]     at emitOne (events.js:77:13)
     [exec]     at Logger.emit (events.js:169:7)
     [exec]     at Logger.emit (/opt/build/tools/node-v4.5.0-linux-x64/lib/node_modules/bower/node_modules/bower-logger/lib/Logger.js:29:39)
     [exec]     at /opt/build/tools/node-v4.5.0-linux-x64/lib/node_modules/bower/lib/commands/index.js:40:20
     [exec]     at _rejected (/opt/build/tools/node-v4.5.0-linux-x64/lib/node_modules/bower/node_modules/q/q.js:797:24)
     [exec]     at /opt/build/tools/node-v4.5.0-linux-x64/lib/node_modules/bower/node_modules/q/q.js:823:30
     [exec]     at Promise.when (/opt/build/tools/node-v4.5.0-linux-x64/lib/node_modules/bower/node_modules/q/q.js:1035:31)
     [exec]     at Promise.promise.promiseDispatch (/opt/build/tools/node-v4.5.0-linux-x64/lib/node_modules/bower/node_modules/q/q.js:741:41)
     [exec] 
     [exec] System info:
     [exec] Bower version: 1.3.12
     [exec] Node version: 4.5.0
     [exec] OS: Linux 4.4.0-24-generic x64
     [exec] bower sweet-material-table#a46795e318             resolved git://github.com/nuxeo/sweet-material-table.git#a46795e318
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 29:10 min
[INFO] Finished at: 2016-12-06T12:14:29+00:00

[INFO] Final Memory: 1601M/3286M
[INFO] ------------------------------------------------------------------------
[WARNING] The requested profile "qa" could not be activated because it does not exist.
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-antrun-plugin:1.7:run (gulp-build) on project nuxeo-salesforce-web: An Ant BuildException has occured: The following error occurred while executing this line:
[ERROR] /opt/jenkins/workspace/Deploy/IT-release-on-demand-build/nuxeo/addons/nuxeo-salesforce/nuxeo-salesforce-web/build.xml:36: exec returned: 1
[ERROR] around Ant part ...... @ 4:250 in /opt/jenkins/workspace/Deploy/IT-release-on-demand-build/nuxeo/addons/nuxeo-salesforce/nuxeo-salesforce-web/target/antrun/build-main.xml